In For All Mankind, TWOK would be impossible. In the remote chance it would happen, it would be unrecognizable and probably nowhere near as good.
The Enterprise would be the Phase II Enterprise. If Ph2 ran from 1977 to 1982 and TWOK came out in 1983, those sets as were would've been laughed at on the Big Screen. Robert Wise gave the sets an extensive makeover for a reason.
Xon would've been in Phase II instead of Spock. Which means "Star Trek without Spock!" goes from unimaginable to something they'd already done for five years. So, no Spock in TWOK, and no Harve Bennett offering to kill off Spock as a hook to get Leonard Nimoy involved. In fact, no Harve Bennett at all. More on that later.
The script for a Star Trek Movie would've been written in-house by Phase II writers, just like the script for the first TNG Movie was written in-house by TNG writers. And they likely would've come up with a very different idea, that they would've rushed through the creative process, just like what happened IRL over a decade later with Generations. The script for TWOK was put together from the best parts of several different scripts written by several different writers.
A first Star Trek movie in For All Mankind would be a cheap-looking rush job put together by TV writers, a TV director, and it would be something that Gene Roddenberry would approve of. Because I think what would've happened on Phase II would've been similar to what happened on TNG. Gene would be heavily involved at first, then less involved as time went on. Only difference is he'd still be alive, wouldn't be in such poor health, and would have more power than "Consultant". He would very much be an Executive Producer. Which means no need to bring in Harve Bennett to replace him. And even if Harve Bennett (who was hired by Paramount in 1980) was brought on as a Co-Executive Producer similar to the way Rick Berman was, he wasn't on the same page as Gene Roddenberry at all on the direction Star Trek should go in, so he wouldn't have lasted long on Phase II in any scenario. Forget about making it to the movies.
So, basically, it's a whole other movie. TWOK isn't TWOK and the TOS Movies go in a very different direction.