Yes exactly. Why wait on a mod to give it to us and instead gain some measure of appreciation and goodwill from fans of the old BG games by just giving us a togglable option to raise party size upto six just for single-player? It really won't even cost them anything because as I said they could provide a disclaimer saying the game is optimized for four so increasing party size can unbalance the player's game experience, then leave it upto us to decide whether that is worth it for us.
