Was St. John referring to schismatic bishops in describing the Antichrist in 1 John 2:18-19?
Anything is possible, but I do not believe so. In fact, the Church does not know who the Antichrist will be until he shows his ugly head as such.
The problem with prophecies in general is that it is almost impossible to know the correct interpretation(s) to them until the actual time of fulfillment is upon us. This passage of St. John is no exception.
18 Little children, it is the last hour; and as you have heard that Antichrist cometh, even now there are become many Antichrists: whereby we know that it is the last hour.
19 They went out from us, but they were not of us. For if they had been of us, they would no doubt have remained with us; but that they may be manifest, that they are not all of us. - 1 John 2:18-19
Many Early Church writers believed the Antichrist would be a Jew. Many believe that The Antichrist Will be a Jew Some modern interpretations lean towards the interpretation of an anti-pope or even a bishop. The traditionally held point of view is that held by the Early Church. In any case, I say that it is impossible to know until he manifests himself.
Prophesies of the Antichrist
By Early Church Fathers
St Cyril of Jerusalem 315 - 386 AD
"Antichrist will exceed in malice, perversity, lust, wickedness, impiety, and ruthlessness and barbarity all men that have ever disgraced human nature. Hence St. Paul emphatically calls him `the man of sin the son of perdition, the wicked one, whose birth and coming is through the operation of Satan, in all manner of seduction and iniquity.' (2 Thess., 2). Through his great power, deceit and malice he shall succeed in decoying or forcing to his worship two thirds of mankind; the remaining third part of men will continue true to the faith and worship of Jesus Christ most steadfastly. But in his satanic rage and fury, Antichrist will persecute these brave and devout Christians during three years and a half, and torture them with such an extremity of barbarity, with all the old and newly invented instruments of pain, as to exceed all past persecutors of the Church combined. He will oblige all his followers to bear impressed upon their foreheads or right hands the mark of the Beast and will starve to death all those who refuse to receive it."
This one shall seize the power of the Roman Empire and shall falsely style himself Christ. By the name Christ he shall deceive the Jews who are expecting the anointed and he shall seduce the Gentiles by his magical illusions.
St. Irenaeus 125 - 202
The antichrist will deceive the Jews to such an extent that they will accept him as the messiah and worship him.
The disciples of the apostles say (from oral tradition) that they (Elias and Henoch) whose living bodies were taken up from this world have been placed in an earthly paradise where they will remain until the end of the world.
At the time of his reign antichrist will command that Jerusalem ne rebuilt in its splendour and will make it a great and populous city, second to none in the world and will order his palace to be built there.
St. Methodius of Olympus 250 - 311
"In the last period Christians will not appreciate the great grace of God who provided a monarch, a long duration of peace, a splendid fertility of the earth. They will be very ungrateful, lead a sinful life, in pride, vanity, unchastely, frivolity, hatred, avarice, gluttony, and many other vices, [so] that the sins of men will stink more than a pestilence before God. Many will doubt whether the Catholic faith is the true and only saving one and whether the Jews are correct when they still expect the Messiah. Many will be the false teachings and resultant bewilderment. The just God will in consequence give Lucifer and all his devils power to come on earth and tempt his godless creatures...
St. John Chrysostom 347 - 407
"Antichrist will be possessed by Satan and be the illegitimate son of a Jewish woman from the East. This world will be faithless and degenerate after the birth of Anti-Christ”.
Sometime ago I answered this question: How can one identify the Anti-Christ; can he be a Bishop opposing the Papacy in relation to 1 John 2:19-20? My post indicated the possibility as such:
A prophecy of St. Francis of Assisi seems to indicate the that either the Antichrist or one of his satellites could be an anti-pope elected uncanonically. Thus he would be at Last a bishop, if not a cardinal.
Prophecy of St. Francis of Assisi (d. 1226): “There will be an uncanonically elected Pope who will cause a great schism, there will be diverse thoughts preached which will cause many, even those in the different orders to doubt, yea, even agree with those heretics which will cause my Order to divide, then will there be such universal dissensions and persecutions that if those days were not shortened even the elect would be lost.” (Rev. Culleton, The Reign of Antichrist, Tan Books, 1974, p. 130.). Some believe this prophecy referred to the controversy surrounding the election of Pope John XXIII and Cardinal Siri. But it could refer to the next and last pope (Peter the Roman). The last pope may just cut Catholics loose from unity and the papacy, causing total disruption and confusion. - Malachy's Prophecies - The Last 10 Popes
In any case, time will tell, so please be patient.
As a little side note there is some speculation that Pope Benedict XVI believed we are in those days now. The Mystery of Evil: Benedict XVI and the End of Days (Meridian: Crossing Aesthetics)
In 2015, Pope Emeritus Benedict XVI wrote a letter to Catholic statesman Vladimir Palko, urging prayer against the “expanding power of the Antichrist”. (Benedict XVI: It Is The Time Of Antichrist)
You may wish to see the following YouTube video: Pope Benedict says Time of the Antichrist is now... Is the Pope right?
Catholic interpretation will vary, but once the Antichrist shows his head, the gig will be up and we will know!
The following articles may be of interest to some: