Due to tradition in DoS larian games, Coop-MP, and because most D&D 5 campaigns are about 4 to 5 players (and they said that they are based in tabletop) I think they are going to settle around a party of 4-5.
But I also think that sooner rather than later will appear a mod to make a party of six anyway, like in the previous games of Larian. They should spare us the wait and make an option to have a bigger party =P
