"The preceding guidelines assume that you have a party consisting of three to five adventureres... If the party contains six or more characters, use the next lowest multiplier on the table." - Page 83 D&D Dungeons Master's Guide
5e considers 4-5 to be standard while 6 or more being optional, totally up to the players and DM for party size. So Larian at the very least can give us max 5 party members if they're being picky with the rules. The reason why many players want the option (keyword option), is because it was an option in the original BG 1 and 2. This is a Baldur's Gate game, doesn't matter who's developing it. I wouldn't mind more elements from the original BG that would further improve BG3. (Party management and maneuvering being a few to list) I also would like to mention that many official WofC D&D adventure modules of both current and past editions are geared for 4-5 and/or 4-6 players. If you want "lore" to further prove my point, take a look at Drizzt companions. He has 5 total in his party. So what if players wanted to have fun and roleplay as Drizzt in BG3 and (hopefully have an option later to add fully other customize companions) his companions from the books?
2. Time management.
The fact that I have to sit and watch my clock during enemy turns against my party of 4 is bogus. For example: Goblin camp. That was about 25 enemies which would be considered a platoon (18-50 soldiers) against my 4 companions which is not even considered a squad (6*-10 soldiers), So already players are watching their clocks for the enemy to take their sweet time in current Early Access. If I had those extra 2 members, I would've had more chances taking out Goblins quickly.
3. Difficulty Levels
If players want a challenge, you have every right to do that and the option of 6 companions will not sour that experience. I honestly think the game should reward players who decide to take these challenges for a smaller party, just like in the original BG. The same amount of experience will be earned for encounters but if your party is smaller, each companion gets a bigger piece of the pie. So far it seems that the game rewards the same amount of exp. no matter how big or small the party size.
4. The game world is not designed for a bigger party
I'd beg to differ. Most battles have a large number of opponents and there is plenty of space for 2 more party members. If a warlock can have their minion and a ranger can have their pet in the same party of 4, It can fit more than four or even 6 playable characters in practically every area. For many of the old-school BG players. Remember Firewine Ruins and how claustrophobic it was? You almost had to move the party in a single file line in that dungeon. BG3 EA hasn't had any dungeons or areas as claustrophobic as Firewine Ruins and if they did, I'm sure it would be a challenging dungeon. Also, I hope to God Larian fixes the party movement and controls.
I don't see how an optional party of 6 would sour your experience if you really hate that idea. In fact it gives you more options and variety on how you want to approach the game. I thought that was the whole reason why we love RPG's the variety of possibilities and customizations.
Larian, if you're reading this, at least let us know why this wouldn't be possible. Many people who don't like the idea say because it's also "balancing issue" and needs a lot of resources. I'm positive that is an issue but if that is true then let's hear it from the horse's mouth and let us know why.