They should have included an option in character creation to choose between a 4 and 6 party limit (for EA only of course), that would have been great at launch and would have supplied feedback from hundred's of thousands of people which cant be ignored what ever the results would have been, unfortunately that ship has sailed, now you have what 20k people playing?? that might not be enough to change their minds if they believe these 20k dont represent the majority
To be fair, that would have required having at-launch encounters balanced for both 4- and 6-character parties. Otherwise the balance and gameplay data, including player experiences, would be way off. Either players using 4-man parties would feel the game is impossibly difficult, or players using parties of 6 would find it way too easy. Given that (I assume) Larian is using EA to test encounter balance, having two party limits seems like it'd just make everything more difficult.
This sounds like something to try once they've gotten a handle on how to balance 5e encounters, around when they're testing different difficulty levels and have decided more about the various acts' level caps.