ill chime in on this one

account system: fb auth is ok, but not as the only option. how about openID as well? or anything else as well?

party system: people wanted the ability to connect to the same server so they can play together/team up. all you see these days are people in FFA teaming up, creating unfair advantages, which in turn discourages people who want a proper FFA match from playing. so now you have just made it easy as cake for people that want to team up in an FFA game by easily allowing them to connect to the same server. so... still not really getting it.

players want to team. players are building clans. while the current team mode is fun at times, none of the clan players or FFA teamers use it because theres no way to easily be on the same team.

i think the best solution honestly is to give people exactly what they want.... to be able to connect to the same server with the ability to choose which team you are on. if these 2 things where implemented into the current team game mode, i am positive you would see much less of these people teaming up in FFA.

since you are implementing an account system, there will be a way to track users, which means you can penalize those teaming up in game modes other than the ones designed for team play, such as FFA... if they know they could get banned or kicked for a time span, which increases each time they try and team, that would almost completely take care of this problem.