But ... let decide the players, I would like it with optional 6. Even without extra modding there were already old screenshots of a very old stage of baldurs gate 3 showing 5 player portraits. Hah!
While our party will consist of 4 people it seems there will be possibility for more units to temporary join our team. There are summons, pets, familiars but also temporary quest companions, if I understood Larian correctly. So it's possible we will have 5 or more characters in our party in certain situations.
Do you have a source about followers that may be companions ? This could be great but don't really remember about it.
Anyway temporary followers is not really the same as companions. As many players, I like management and a party of 6 instead of 4 is 150% more management
It could be great if the temporary companions you're talking abouté could become real "classical" companions (meaning : without the caracteristics of origin characters)