There is already a mod out for the beta that increases party size as well, for those who are interested in BG3 but want a full party of 6 or more. I can only hope the mod authors keep up with it, and release a version for the full game in August.
I'm replaying DOS2:EE right now, with a 7 person party (6 NPCs and a custom Summoner just because) and it's great! It's easier of course, but DOS2:EE has pretty nice difficulty settings to deal with that. Eventually I'd expect BG3 to have the same thing. It'll be 6-8 person parties for me in Baldur's Gate 3, hopefully within a week of the retail release.