I think 4v4 is too small as you don’t get the opportunities for more advanced strats that you have with slightly larger team sizes. I think 5v5 though offers a decent compromise, still small enough where you can get people together consistently, but large enough for a little more variety in strats.
As an example, without 5v5 we may never see operatives in competition except at hack objectives, but give the team a little room and the added defensive traits they’ve been given will more likley be used.
4v4 ETQW, meh, boring compared to 6v6 just because of all the added strats and things the teams were forced to contend with. Granted, there’s probably not nearly as much difference between 4v4 Brink and 5v5 Brink as there was between 4v4 ETQW and 6v6 ETQW; and yes, I know a big part of the difference between those two modes was one had vehicles and one did not, but I think the concept still applies just on a smaller scale.
I don’t think there will be issues with people able to field teams of 5, and the added depth and subsequent excitement for the spectators will probably be worth it. Also, with slightly larger team sizes you get more opportunities for less skilled players like myself to actually play since there’s more room for their team mates to help pick up the slack
Seriously, more room for new comp players to learn the ropes.