I'm sure a lot of people would. Sure, folks like to undersize stuff, but to me it feels wrong and give an option, I'd feel compelled to do it as the balance would be around six.
And bringing six now as it is would make a lot of the harder fights easy.
I honestly don't expect them to change it. I hope they don't, but if they do, meh.
So you're saying that, if 6 was an option, you'd feel compelled to bring 6 people and either: 1.) Larian rebalances the game around 6 (possibly using split exp, possibly changing encounters) and thus your game balance would be fine, or 2.) Larian doesn't rebalance the game around 6, and thus playing with 6 would be too easy. Is that right?
Obviously option #2 is bad, but are you also implying that option #1 is different/worse than currently being compelled to use a party-of-4? If so, how? Please assume that Larian will NOT balance for a party of 6 by adding more enemies (e.g., WotR Defender's Seige); basically everyone already agrees that's a bad idea so there's no point discussing it.
Adding enemies would just drag out combat in a turn based game. I mentioned an example earlier. They'd have to increase HP a bunch.
If they don't rebalance, 6 will make it too easy. If 6 is optional ill feel compelled to bring them along anyway because "it's obviously intended this way, otherwise they wouldn't have made it this way.". As I'm sure you know, bringing 4 now is optional, as all of EA has been solo cleared, and that's not something I'd do, because it's not intended, just possible.