What if Judaism, Christianity and Islam were all true and part of God's three succesive revelations?

[Rise]

I think God wants to reveal to all of humanity but he is aware that a universal message wouldn't work because people have lots of different mindsets. So he chooses to reveal himself in different ways intended for different types of people.

If God's stated goal is "revealing Himself" (and I agree we see that as a goal in the Bible) then by definition what he reveals at different times to different people will be consistent. Because to do otherwise would be to fail at revealing who He is by giving wrong information that contradicts what He has already revealed. Because, we assume, as the Bible says, that God doesn't change and that God isn't a liar (Malachi 3:6, Hebrews 6:18).

The question you have to then ask yourself is: Is what Islam says compatible with what Christianity says? If the answer is no then they cannot be revelations from the same God. That would either mean that God has changed or that God has lied, which would itself contradict what both the OT and NT have revealed to us about God.

The fact is, Islam is founded on the belief that the NT and OT are full of lies and have been changed. That is what their leaders will tell you about the Bible. They must say this if they want to believe the Quran is true because the Quran is not actually compatible with them.

In contrast, the NT is founded on the belief that the scripture in use at the time of Jesus (still found in the OT today) is true and represents an accurate revelation of God to man. Many scholars like Dr. Micheal Brown, specializing in the Jewish roots of the Christian faith, are able to effectively demonstrate that the NT is entirely consistent with the OT.

His third revelation until now was Islam. He knew that lots of people wouldn't accept Christianity since the idea of a human God was hard to comprehend. So he made a revelation in which Jesus is a Prophet but also is a return to roots to some aspects of Judaism like strict monotheism, etc.

The two claims aren't compatible. Only one can be true. Otherwise God would have to either be changing what is true or lying in one of those instances about what the truth is. More likely is that God hasn't changed or lied but some person has lied about being given revelation from God.

On that possibility, Paul warned us in Galatians 1:8 that we should not believe anyone who comes after him claiming to have a "new" revelation of God that contradicts that which has already been revealed.

I would expect a fourth revelation that would probably be the last one although I'm not sure about that. This fourth revelation would end up converting the rest of world religions into the God of Abraham.

The book of Revelation already talks about that happening. Except it is the anti-christ, the one who stands against God, who tries to enslave the world in a deception that would separate them from God.
He tries to get Christians and Jews to abandon what the Scripture tells them is true in order to accept his new false religion.