Larian Studios Forums Baldur's Gate III Baldur's Gate III - Mega-threads and Guides Party Size Discussion

I just find it unlikely to happen (at release at least I would say) precisely because it adds another component to balancing the difficulties (and therefore adds more work on top of exisiting balance) while the game is still in development and probably it was not something planned.
As for your question... That's on Larian I think. I don't think they've been too clear on what exactly they might be incorporating (to settle some debates) from the feedback and I can understand that, because you may say that you're implementing one thing but end up unable to do so. On the flip side I think it creates a situation when you might feel your feedback is useless, so I do feel they need to be more clear on what they might do and what they won't do just so there would be some clarity.
The issue is that due to BG3 not being traditional Early Access there will be no means for players to playtest later stages of the game, and that's where most script issues will be much more likely to pop up me thinks. Especially if Larian by default enforces fixed 4-party setup at some point similary to DOS2.
Except somebody will be happy to jump in for 6ppl party because they were excited to so it, thinks it's more fitting - just like you, someone who might not have followed the development... and are greeted by a warning that hey, it wasnt really tested and you might encounter issues. Not exactly something what a game should have on release, don't you think? Esp;ecially one that's probably going to be around 100h long. And people will be reasonably pissed at Larian for an incomplete feature. In that case it makes more sense to lay some foundations for modders to work later on rather diverting focus to a mode that was not a priority.
It will only help find issues similar to "the boat killing". As I said, it's unknown what other problems and bugs can stem from altering party size later; something I wouldn't call an imaginary issue bur rather "possible but very probable" issue. Only Larian know and as far as I know, they don't share much on this. I would be absolutely glad to be wrong if Larian actually delivers a functional 6-mode on release though.
Make a properly worked on mode instead of bandaid solution? I don't really see a good middle option.
The issue is that Larian is the developer, not a modder. There are wages to pay, work to be done within some window because they can't be developing forever or run out of money so focuses and sacrifices are inevitable. Modders are usually not restricted by these constraints because they are not a company and installing a mod is always at your own risk by default. So modders can try and do things that the company might find unreasonable in certain circumstances precisely because they're a company. A modder is unlikely to be restricted by having to proft from his mod and can allow work at a slower pace.
From what I see a lot of RPG fans don't necesarily agree what substitiues a good RPG anyway. Take me for example - I value story over deep gameplay mechanics while I still don't want an RPG turning into a purely interactive story while some more old-school gamers would probably prefer much more mechanical depth. Then there's the whole RTWP vs TB, voiced vs silent protagonist, fully custom vs more defined protagonist, origin vs fully NPC companions, true to tabletop stats vs altered stats... the list goes on and on and all these vary from person to person. BG3 by virtue of being named BG3 managed to bring in pretty much every opinion and they're constantly clashing - here, on reddit, on Steam... And because the opinions can be so diverse even within a single group it's an impossible task for Larin to "properly" pick a side in this clashing... outside of their own, most likely.