We talked about the core features yesterday and when it comes to versus mode the biggest issue is getting the netcode up to a level where you can play over the Atlantic and have a high ping w/o any major issues, just as you can do with many other more established games, this is not as easy as it sounds. Those issues are far less in coop, cause you fight AI and if it's lags or gets a bit desynced it won't really effect the gameplay - people just don't feel cheated out of a kill in the same way. That's our biggest issue getting a solid versus experince.
When it comes to amount of players, I say we probably need to restrict the games split view feature to 4 but, other than that, it's up to lobby and HUD design as the limit, we talked about more than 4 players, 6-8 would be really cool to see.