Clearly, there is division in opinion. Not all protestants will agree.
For many protestants, the Kingdom is looked forward to as a literal reign of Chirst on the Earth in the millennium, hence the Millennial reign of Christ. This view holds that the kingdom is only here "in a mystery", such as a seed of the church, and that the outward Kingdom will be here through Israel as chief among the nations, fully healed of her backsliding.
On the other hand, many see the Kingdom as a realm of God, and not aa an outward governmental system. These view the Kingdom as a reign of God to which Israel was offered a part, they rejected, and so, by and large, it went over to the Gentiles.
There are two issues with your question.
First, some disagree that "the church" is the Kingdom. They would say the Kingdom was offered to Israel, they rejected it, and it will come again at His Second Coming. They would claim the church is a parenthesis in the plan of God until it comes back to the Kingdom with Israel. Whatever the church is, they claim, it is unforseen by the Old Covenant, and is not the Kingdom. Not all hold to this, but it is popular.
Second, not all agree that Israel was the Kingdom. In Acts 1:6, the disciples asked Jesus if He would at thay time restore the Kingdom to Israel, indicating that it was not the "Kingdom" at that time.
From these two points, the question of whether the church and Israel are separate kingdoms is probably a "Yes" on the basis that the church and Israel are two separate entities, but "No" from your development of whether God is onlyndealing with the church, and has completely discarded Israel.
From what I can gather of your question, it seems to be 2-fold.
- Did the church replace Israel in the plan of God?
- Is the church the Kingdom Jesus talked about?
As to the first, it has become decidedly unpopular in many protestant groups to adhere to "replacement theology", that the church has replaced Israel. Rather, as Paul argues in Romans, Jewish branches were broken off an olive tree, and Gentiles were grafted in, symbolizing the Jews. As such, the "root" of the church, if you will, is still the Jews. Some still hold this replacement position, but it seems without support.
The issue here is tied with the second point. Both agree God is not essentially done with Israel, but the debate is in how God deals with His people.
Those who say the church is not the Kingdom, that it refers to Israel, obviously do not think that God is done with them. They go so far as to say God still deals with them separate, and He will do His own thing with them in its time.
Those who believe, however, that the church represents the Kingdom would hold that Gods heart is still for them, but that they all must be born again in Jesus, that is, become part of the church. This does not, however, mean that God does not regard the nation of Jews as nothing at all. Although there are a variety of opinions, some hold that Pauls words in Romans 10-11 are prophecy concerning their coming salvation. This goes hand in hand with the promises that say that as long as sun and moon, seedtime and harvest, all endure, Israel will be a nation before Him.
This last case seems the most plausible to myself. In the end of Ezekiel 38-39, which details the "Gog-Magog" war, the end result is a regathering of Israel, a nationwide salvation, and God pouring out His Spirit upon the whole nation. As this speaks of the outpouring of thr Spirit, thisncould not have happened before Pentecost, and as Israel waa under judgment, it wouldnt have been between then and 70ad when the Jews were scattered. Likewise, since it speaks of the regathering, it could not have been before 1948, as the Jews were scattered until then. In this regard, it seems, the, although salvation is onky in the church, the church has Jewish roots. And, it appears as though God will indeed have mercy again upon His covenant people, and will see them brought into the salvation which birthed the church.