Apparently they CAN combine threads. A bit wonkily since everything is just kinda jumbled together now but reading back through it all I guess it's not too terribly incoherent.
I wanted to try and summarize a few things, maybe, I'm not sure it's possible after reading most of the day with a brain turned to jello now... but I'll try for a few things I think at least.
1. Char Number Options - 6 players doesn't have to detract from those that prefer less. Having the option there would be really nice though for those that DO want to play with a larger party size. You can always play with less but you can't just add more if it's not build into the game. Yes mods are possible however I always greatly prefer something actually be built into the game, primarily for stability but also overall functionality & integration. Well after DOSII had been out we tried using mods to increase party size and monsters etc and it was WONKY in multiplayer. We didn't even make it off the island before the game was so broken it wasn't possible to progress. In singleplayer we were able to make them work but it took a few play through to figure out how to balance monsters so that char were about the same level they should be and combat was still challenging. It wasn't THAT hard though such that some people make it sound like it would be impossible or take forever or something. Two regular arse casual gamers didn't have too bad of a time figuring it out...
2. Story - My gf has never played the original baldurs gate games, however she has played the crap out of DOSII. What was the first thing she wanted to do with the game? Mod it so she could have ALL the story characters in her party at once and do all of their stories in one play through. (This required messing around with balancing mods quite a lot, which is another issue.) Neither of us minded bigger battles, more monsters (Some people actually enjoy more/longer combat when it's well implemented.) Of course those that want less, can always just do the game with less characters, 2, 4, whatever. It was interesting to me how much she really liked all of the characters and their stories. She also bought the book with more of the stories they have. Would she have liked the game as much with less characters? I guess I don't know. Would she have liked it as much more? I again don't know but the answer logically seems yes, and it wasn't so much the number of playthroughs to achieve that because she's played through it a ton of times, apparently she just likes having more characters in the story in each of those playthroughs.
I thought it was interesting being that she's not really a big gamer but absolutely loves that game and has played it multiple times now with those mods on for basically more everything; more story, characters, monsters, combat. She has no issues managing what like 9 inventories and does so happily (with the special container mod on). Is this for everyone? Of course not. But she absolutely loves to play it that way so if the options were there, some people would enjoy them as opposed to the idea that anything over 4 is heresy and micromanagement sin. No one has to play that way or another if there are options, and options would be nice to have at the start.
3. Slog / Combat / Scaling / XP - There could be various difficulties & or a slider for number of monsters even & or a slider for monster stats, or all 3. Recommended presets for various party numbers. Or whatever combination of those options they wanted to present with. Experience can also be however they want to customize in relation to party based on the options available. Like you could adjust for larger party size with simply more monsters and thus there is your extra exp so chars are basically same level as a 4 char party would be at any given time so that exp can be split among party members but you can make it basically same for larger party by just adding more monsters, or you could have same number of monsters and just make them stronger & worth a little more XP to spread out relatively the same. Use a 2 char party with the normal 4 char number of monsters and level a bit faster if you want to play 2. Or try even more monsters and level even faster if you can survive. The slider could even be adjustable just like difficulty level at any time in between battles maybe. Doing these things would be like basically taking a lot of the best mods for DOSII and building them right into the game which would be FANTASTIC and help to suit someone that wants to play solo as much as those who would prefer all the wonderful flavor of a 6 character party along with a level of challenge the player prefers.
4. Time / Resource / I want mine no not yours - As others have pointed out many of the arguments against 6 characters seem to be based around being ok with 4. That's great you get what you want and you don't want it changed, but what about everyone else? A lot of people that I feel kind of mainly representing a younger demographic have primarily only had 4 player games, while a lot of the older games, ones us old farts remember and love, were 6. I've stated before that frankly I've been quite tired of 4 players seeming to be the unspoken maximum number of players for like 10+ years in games now and it drives me batty. Maybe it won't matter as much to me because I literally might not be around but that's been something that has irked me for a while as a sort of trend. I come from a large family and we frequently pass on games that are limited in the number of players because too many are left out. I digress. Anyway, arguments that time could be better used for this vs that is a matter of opinion and clearly there are lots of people that would definitely like some of that time/resources dedicated to at the very least making 6 characters an option and I think the option is the best compromise. Or depending on how XP / monster scaling possibilities / monster number possibilities maybe it doesn't so much have to be an option as the other options. You could have up to 6 and adjust the difficulty/number of monsters/monster strength however you like for the number of characters you plan to run. Everyone is happy. Or should be, anyway. No one HAS to run 6, but you can, there are 6 slots available and you can fill them all, or run with as few as you want. No one HAS to get more, or less XP, or more, or less combat/monsters, but you can. (Suggested presets might be nice to kind of help maintain homogeneous party level in various areas so battles don't start to get too easy / party over leveled with large parties.) If that seems like too many options then they could perhaps just integrate it all into the difficulty mostly or just have difficulty + monster number OR difficulty + monster strength scaling rather than all 3. Or, perhaps not best but simplest, build it all into difficulty.
So some may say, well I'm ok with 4 so I just want more of whatever they can add ignoring spending any time on accommodating six, but the counter argument for everyone who would like to have six is just as valid and actually imho a bit less selfish since players who want to play with 4 don't lose their ability to do that. PLUS, you get the chance for more characters (& their stories) to go through the story within a single play through so any potential theoretical loss of story can be mitigated by having a few more party members making things more interesting & more different interaction possibilities.
Of course, this is also supposed to be BGIII, not DOSIII. Because of the turn based combat, it's going to look/feel potentially a bit similar. To me, other than obvious D&D rules & world, one distinction that also harkens to the originals could be six character party possible.
I'm sure I could have done a better job summarizing a left some things out but after reading for the better part of the day I think my brain is going numb.