The max number of players is largely going to be determined by early access results.
Basically, if each player has 10,000 units what kind of bandwidth is needed by each player to handle that in a fun way?
I've played several games vs. AI and with AI vs. AI. The rounds have lasted 30-120 Min. I was never even close to 10k Units. The highest unitcount was around 750. To hit the 10k units with the current build, you would have to play 4-6? hours I guess. I don't think that onlinegames took that long
Well, you could hit the 10k faster if you just build T1 units