Parmandur
Book-Friend
I think they will know the general shape of the revision by the end of next month, once they get the survey results for Races, Backgrounds and the general rule changes computed. Class changes probably won't make that big a difference to their 2023 book plans.I think it is a clear indication that a main design goal of One will be that adventures in particular will be compatible. Broadly this seems possible because if you use One characters AND One monsters (including MotM monsters) then it should all work out -- theoretically of course. What is likely less compatible is "core" 5E material and pre Tasha's PC facing stuff (not sure about Xanathars considering they included it in the gift set with MotM and Tasha's).
Whether this goal survives playtesting of course remains to be seen. They may find that an overwhelming majority of players want things that aren't compatible and that goal will go to the back burner.
If anything, theybseemd to be more than willing to throw out any changes and go back to 2014 standard if people want to. Doubtful we will see anything more radical.