Some facts about party size in D&D 5e, just to make sure we're all on the same page. If I get something incorrect please correct me.
DMG pg 83: CR and encounter building "assumes that you have a party consisting of three to five adventurers." Specifically, 3 to 5 players are treated as equivalent, whereas 6+ and 2- require additional calculations to determine encounter difficulty.
All Adventure Modules suggest either 4, 4-5, or 4-6 players. No modules that I'm aware of suggest 3 players.
In summary, while all party sizes are technically allowed, the standard seems to be 4-5 players with 6 or 3 less common but still explicitly encouraged by official D&D books.
Personally: +1 for allowing a larger party size where split exp is used to balance parties of all sizes, as long as it's an option in settings and not in-game. I want the base game to remain balanced around a party of 4 and I don't want to, by default, be allowed to have 6 people in my party.
1. I do hope they give a party of 6 setting. However, I do not want the game balanced around their janky homebrew monsters and rules and then have them give us party of 6 and have it be a totally sucky experience.
2. The game is only balanced currently around party of 4 because monsters and rules are not genuine 5e. There is so much homebrew. If they were based more on 5e, the battles would be really hard for party of 4.
Give me option for genuine 5e stats and rules and option for party of 6, and we should be good. Hopefully.
My big fear is they'll balance around homebrew and then give us 5e, and it'll be so difficult even with party of 6 that it won't be fun.