Increasing the default party size is not such a simple matter. I've done one playthrough with a party of 6 on Patch 6, and with this many characters you can steamroll almost every encounter using basic attacks and little else. For a proper party of 6, the entire game would have to be rebalanced, most if not all encounters remade.
Don't get me wrong, I'd like a bigger party as well, if only to see more story, but it's not as simple as "just making it official".
Well, aside from the fact that they COULD rebalance it (after all nothing so far is final, plus they ALREADY plan to have multiple difficulty settings) there's also the option to let this be a problem of the players. If they want to play with six characters(and I want it, too) just let them do it.
But we already talked ALL these arguments and a lot more for hundreds of pages at this point in time, as the gargantuan mega-thread on this specific topic can attest.
The option to use mercenary rather than companions is an already-confirmed upcoming feature, though, so that shouldn't be a worry for anyone.
Party control in Baldur's Gate 3 is a complete mess that begs to be addressed. SAY NO TO THE TOILET CHAIN
