\ ... And dnd is written for parties of 3 to 4 players. You can have bigger parties but it quikly muddies the waters with regards to balance. It very easily becomes to easy or to hard if you muck that up. So giving us an option to do it would work imho. Maybe make it be tied to a higher difficulty or something or just place a warning that the game might be easier then it was intended to be. But more options for the player is rarely a bad thing and I couldnt totally stand behind the option of allowing 6 man parties.
I've heard that repeatedly (the 4-party 'ideal'). I assume that's because CR was originally based on a group of 4, and it involves some work for a DM to rescale encounters in P&P. But that really doesn't mean its intended for 4 players only. I have always played with larger groups. Yes, 5E is more versatile with class roles, so you can get away with fewer players, but really that by no means precludes or limits player numbers. I have also DM'd and recently played with 6 players in a 5E campaign. It is absolutely doable, so I really don't think that's a reason not to support more than 4 players. They could quite easily target a 6-person party and have everything 'scaled' - or as others have argued, if the XP awards are split, then the party level would self balance (or could ne made to) anyway and over-levelling on core content should not be an issue.
I would prefer of 6 (or at least 5) person party. I find 4 too limiting, even if I can cover core roles with 4. It seems like an artificial optimization exercise. I would like my ranger, cleric, wizard, paladin, rogue etc. as I did before.
That's the thing. I've play tested scenarios for BG3 in Tabletop. Every encounter is designed for a larger party. Party of 4 is Deadly for almost each and every encounter while Party of 6 is not.
Take the first encounters with imps. Party of 2 (MC and Lae'zel) against 3 imps is suicide using proper D&D 5e stats. However, if you START with Party of 4 and add Lae'zel, THEN 3 imps is a fairly decent Tutorial fight at Level 1. Same is true for all the fights in the Prologue. The first beach fight with 3 Intellect Devourers is also suicide with just Party of 2 (MC and Shadowheart), but a party of 4 with Shadowheart (making 5 characters at Level 1 or 2) is doable. It's still tough, but if you know to keep them at a range, you shouldn't have an issue with party of 5.
Then take on Gimblebock and his 3 friends plus the 6 mercenaries inside the crypt (total of 10, but spread out). That's a bit more rough for a party of 4 to do all without taking a Long Rest, especially if you just got done with the 3 intellect devourers at the nautiloid AND if you actually did fight the fishermen. But, with a party of 6 (4 customs + 2 origins), you can face all of them before needing a Long Rest. It all makes more sense with a party of 6 so that by the time you reach the grove, you likely won't have Long Rested even once, but you will have probably Short Rested once or twice. From a story perspective, this makes more sense.
Then take later encounters. Hag's lair can be done all in one playthrough without needing to fight redcaps, Long Rest, fight Masks, Long Rest, fight Hag. Spiders can also be done in one playthrough without fighting ettercaps and first group of phase spiders, Long Rest, fight matriarch and her minions.
Originally, outside the Necromancer's Lair, they used to have like eight skeletons that you had to fight. But the fight was so hard for party of 4 that they had to now nerf it to like 3 skeletons.
The gith fight is still complained about probably the most by players because it's too hard. Party of 6? So much more doable. Even the goblin camp massacres and so forth are so much less frustrating and take a lot less time when you have a party of 6 - so you get two more characters per round that can go and kill goblins, ogres, bugbears and so forth.
The whole experience is just a lot better with party of 6, and if they did that, they could use proper D&D stats and rules and the whole game would be more balance and fun.