Just to add my point of view to the discussion, while like most of you guys I would preferer a party of 6 for multiple reasons most were mentioned before so no point in going over them again. Larian has already acknowledged that many fans want a 6 player party and they still decided to go for a 4 party build because they felt it was the "sweet spot" so asking them to change to 6 party and rebalance the whole game in very unlikely, I think we should be more realistic with our requests and go with what the OP suggested - they continue to follow there vision and create the game for a 4 man party, add a option in menus to unlock a 6 man party with a pop up notifying you that the game was balanced for 4 man party and difficulty level is untested for this build. this has a much higher chance of happening if they see the demand for it.
and for those thinking that what's the point of a 6 man party if combat is balanced for 4 - well i can give you at least one after act 1 we need to choose who moves on with us to act2 and who is left behind, this way we get to take more companions with us - more companions quests to do, better RP and banter etc..
