ATM, I am playing through XCOM2, and IF Larian was going to do a larger group size, I think they should check out how this game does it. Basically you have to activate the ability through leveling (this could actually be a way to make the camp more interactive) through leveling up your ship, and building a war center that has that as a perk. In this case, they can have you put points in growing your camp, and activating first 5 man then 6 man as you build your camp. I doubt it would happen, it is way to late in the game for them to do such a major change, but it would be nice.
+1 really good and intriguing idea - it does seem like the camp is set up perfectly for such an approach
(as an aside xcom2:WOTC is 75 percent off on steam until the 18th for interested parties)