I'm an adamant fan of FFA.
When I'm not working in an organized unit playing team-based matches, I'm demolishing as many people as possible before I either die, or run out of ammo. As stated before, the Mech3 Zone MP would have been nowhere near as fun without all the random FFA matches thrown in.
It's easier to pick up a game in a FFA where all odds are against you, then rely on Pubs to guide you to success. If it is too much work, I don't mind having it added in later, but I think FFA is a must at some point because not everyone wants a team. At least for the SA mode there should definitely be FFA at some point because it's also geared more towards the casual player to just wants to hop in and kill a few people, rather than have a team's win depend on whether you stay or go.