I'll attempt to play PA with that many people. I admit I have not done so in that game because the last time I played it was...last year? And it did not work so well.
Still sounds like it would be a lot of chaos.
chaos isn't a bad word in an RTS lover's dictionary.
no seriously, though. it can be a lot of fun. Most of the time these sorts of games are set up in FFA. on FAF 12 players is the maximum and sometimes we like to do 12P FFA on the 12P version of setons. it's over quite fast because of the close proximity but it's a lot of fun. Also FAF has a shared armies mod : http://forums.faforever.com/forums/viewtopic.php?f=45&t=8508 (now this obviously needs voice chat)
this is probably the best thing to try 12P out with. you can even play it as a 1v1 on a small map. it's ridiculously fun.
it can also be really fun to play 12P in FFA and with murder party activated (the one where at regular interval's everyone's target to kill is changed)
why not phantomX.
on PA it's generally important to do these big number of players matches on a single planet as PA has a balance problem that tends to accentuate itself with more planets. On PA the best setup for this is team play. 3 - 4 teams (and preferably with shared army (and obviously over voice chat)).