I have learned more about conjecture. Link: You know what probably happened?
So, my understanding is as follows.
1. You know what probably happened? 2. You know what I think probably happened?
Both sentences express a conjecture equally well. The difference is not semantic. It is mainly stylistic. 'I think' just softens the conjecture a bit. It is already clear that the first sentence is a conjecture because of the 'probably'.
I've understood the above feedback from a good person who is legatrix.
3. You know what would probably happen?
This sentence No. 3 is different. It is back-shifting by 'would usage.'
I mean, I expected "Something will probably happen" in the past. As time goes by, I can say the past event which, I expect, was likely to take place. Hence, I guess sentence No. 3 is similar to the under one.
= You know what was probably gonna happen?
Do I understand exactly?