Is the Eastern Orthodox opposition to the immaculate conception an innovation? YES
In light of their own Tradition which already celebrated the Immaculate Conception having their own liturgy during the early Church Father time.
Fr. Casimir Kucharek in his magnus opus "The Byzantine-Slav Liturgy of St. John Chrysostom" (1971; Alleluia Press, pp. 355-357) marshals the evidence that the early Eastern Church did believe in and commemorate the Immaculate Conception of the Theotokos:
*Also, from end to end of the Byzantine world, both Catholic and Orthodox greet the Mother of God as "archrantos", "the immaculate, spotless one," no less than eight times in the Divine Liturgy alone. But especially on the feast of her conception (December 9 in the Byzantine Church) is her immaculateness stressed: "This day, O faithful, from saintly parents begins to take being the spotless lamb, the most pure tabernacle, Mary..."; "She is conceived...the only immaculate one"; "or "Having conceived the most pure dove, Anne filled...." [References: From the Office of Matins, the Third Ode of the Canon for the feast; From the Office of Matins, the Stanzas during the Seating, for the same feast; From the Office of Matins, the Sixth Ode of the Canon for the same feast.]*
Has Eastern Orthodoxy always opposed the doctrine of the Immaculate Conception of the Theotokos, the Mother of God? She is praised in the Megalynarion hymn in the Divine Liturgy and in Vespers and Matins showing the pre-eminence of Mary among the saints:
It is truly right to bless you, O Theotokos, ever-blessed and most pure, and the Mother of our God. More honorable than the Cheribum, and more glorious beyond compare than the Seraphim, without defilement you gave birth to God the Word: True Theotokos, we magnify you.
*How is the Theotokos "most pure"? Most Orthodox would say that she was without sin at the Annunciation, but would disagree that the Virgin Mary was conceived immaculate by St. Anne. Fr. Peter E. Gillquist comments in "Becoming Orthodox":*
This is where the problem starts with some if not most of the Orthodox. The question is when is Mary begin to be addressed "All-Holy" or spotless?
Some or perhaps most acknowledged Mary as "All-Holy" at the Annunciation, and this is where the innovation begin as the Eastern Orthodox upheld Mary's dignity even at Her origin coming from a saintly parents.
No sin, no fault, not even the slightest, ever marred the perfect sanctity of this masterpiece of God's creation. For hundred of years, the Byzantine Church has believed this, prayed and honored Mary in this way. Centuries of sacred tradition stand behind this title.
ORTHODOXY AND THE DOCTRINE OF THE IMMACULATE CONCEPTION OF THE THEOTOKOS—UNIQUE TO THE MODERN ROMAN CHURCH OR ANCIENT EASTERN TRADITION?
So, the problem really is Eastern Orthodox must revisit one of their Great Theologian and also acknowledge by the West as Doctor of the Church. The wisdom & teaching of St. John Damascene can harmonize the Catechism of the Catholic Church and Immaculate Conception Dogma even the teaching of the Great Saint St.John Paul II saying "Absolute Enmity".
The question is where does enmity started between Mary and Satan? The one who infected Eve with his malice and tempted Adam to commit the sin of disobedience.
To believe in Eastern Orthodox that Mary contracted the guilt or was born with a fallen human nature would contradict the biblical teachings and Tradition stating Mary was the New Eve and the New Ark of the Covenant.
Aside from this, the Holy Eucharist is the source of Eternal Life which is "body & blood" of the Crucified Jesus which found it's source in Mary's own flesh & blood.
Jesus said to them, “Very truly I tell you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. Whoever eats my flesh and drinks my blood has eternal life, and I will raise them up at the last day. For my flesh is real food and my blood is real drink." (John6:53-55)
With Jesus not compromising this hard teaching even if all the Apostles left Him, how come the East would embraced that at some point in Mary's life her flesh was "touch" by Satan?
So, if St.John Paul II stated the enmity is absolute, meaning there is no window or even a slight event that satan ever "touch" the Blessed Virgin Mary. When does the enmity must start?
We found the clear answer from God Himself after the Fall of Adam & Eve.
Genesis 3:15 Douay-Rheims 1899 American Edition (DRA)
"I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel."
Now let's connect St.John Paul II teaching on "Absolute Enmity" with God declaring "perennial enmity" with St.John Damascene words;
“O most blessed loins of Joachim from which came forth a spotless seed! O glorious womb of Anne in which a most holy offspring grew.” John of Damascus, Homily I (ante A.D. 749).
"O blessed loins of Joachim, whence the all-pure seed was poured out! O glorious womb of Anna, in which the most holy fetus grew and was formed, silently increasing! O womb in which was conceived the living heaven, wider than the wideness of the heavens."
A Little Treatise on Mary by St. John Damascene
“She is born like the cherubim, she who is of a pure, immaculate clay.” Theotokos of Livias, Panegyric for the feast of the Assumption, 5:6 (ante A.D. 650). - THE BLESSED VIRGIN MARY
492 *The "splendor of an entirely unique holiness" by which Mary is "enriched from the first instant of her conception" comes wholly from Christ: she is "redeemed, in a more exalted fashion, by reason of the merits of her Son".136 The Father blessed Mary more than any other created person "in Christ with every spiritual blessing in the heavenly places" and chose her "in Christ before the foundation of the world, to be holy and blameless before him in love".*
St.John Damascene teaching is the answer to Catechism of the Catholic Church when it teaches Mary was redeemed in a more exalted fashion. How? right at the very seed that St.Joachim poured-out. The generation of the seed coming from St.Joachim is where the "Body & Blood" the merit of Jesus Christ had been applied and preserved during "marital act" and sustain at Anne pure & holy womb by the assistance of God's singular & unique overflowing graces to exalt the dignity of the future Mother of God. In this way it affirmed all the text in Ineffabilis Deus pointing to the original holiness purity of Mary at the very beginning of Her existence. Satan had never touch Mary right at the very seed, the source of Her flesh or human nature. God redeemed the human nature of Mary by purifying the seed of St.Joachim, like a purified gold.
Reading the whole text of the Dogma of Immaculate Conception will open your eyes to a lot of revealed and acknowledge Truth about the purity,sanctity,holiness,dignity,etc. of the Blessed Virgin Mary.
The Fathers and writers of the Church, well versed in the heavenly Scriptures, had nothing more at heart than to vie with one another in preaching and teaching in many wonderful ways the Virgin’s supreme sanctity, dignity, and immunity from all stain of sin, and her renowned victory over the most foul enemy of the human race. This they did in the books they wrote to explain the Scriptures, to vindicate the dogmas, and to instruct the faithful.
This sublime and singular privilege of the Blessed Virgin, together with her most excellent innocence, purity, holiness and freedom from every stain of sin, as well as the unspeakable abundance and greatness of all heavenly graces, virtues and privileges
In like manner did they use the words of the prophets to describe this wondrous abundance of divine gifts and the original innocence of the Virgin of whom Jesus was born. They celebrated the august Virgin as the spotless dove, as the holy Jerusalem, as the exalted throne of God, as the ark and house of holiness which Eternal Wisdom built, and as that Queen who, abounding in delights and leaning on her Beloved, came forth from the mouth of the Most High, entirely perfect, beautiful, most dear to God and never stained with the least blemish.
Note: Read again the Dogma of Immaculate Concepcion and you will find that this document described Mary's purity right at the very beginning from the mouth of God.Why? She is the Woman destined enflesh the Divine Word to dwell among us and also the Woman destined to give house to the Holy Spirit to indwelt in us.
721 Mary, the all-holy ever-virgin Mother of God, is the masterwork of the mission of the Son and the Spirit in the fullness of time. For the first time in the plan of salvation and because his Spirit had prepared her, the Father found the dwelling place where his Son and his Spirit could dwell among men. In this sense the Church's Tradition has often read the most beautiful texts on wisdom in relation to Mary.101 Mary is acclaimed and represented in the liturgy as the "Seat of Wisdom."
In closing, The Eastern Orthodox must upheld the teaching of St.John Damascene in order for them to embraced the Wisdom in the defined and proclaimed teaching of the Immaculate Conception. And he Catholic Church must embraced the teaching of St.John Damascene too in order for them to described & support their Catechism in how Mary was redeemed in a more exalted way.
The Blessed Virgin Mary was redeemed in a more exalted way better than St.John the Baptist even better than the prophet Jeremiah and to all the chosen souls (patriarchs & prophets) whom the merit of Jesus Christ won at the Foot of the Cross had been applied in advance to fulfill the Divine Plan of Salvation.
"For he chose us in him before the creation of the world to be holy and blameless in his sight. In love he predestined us for adoption to sonship[b] through Jesus Christ, in accordance with his pleasure and will— to the praise of his glorious grace, which he has freely given us in the One he loves."(Ephesians1:4-6)