I was just watching this interview with Sven from back in September and they are aware of modders upping the party number, and he implied they would leave that to mods, saying they can offer a better experience with only 4 characters.
Yeah, I know what he said. It's just one of the many times I disagreed with him. I disagreed with him about the brilliance of the chain/unchain system to control the party (see my signature for more details). I disagreed with him on the merits of the armor system in DOS 2. I disagreed with him about a day/night cycle being superfluous and a low priority for immersion I disagreed with him about randomly generated loot being better than unique handìplaced items in DOS 1 and 2.
This is just going to add to that pile. I wonder if even this time the epilogue is going to be the same: with Larian sticking to their guns and then coming back two years later saying "Boy, we were wrong and that feature surely sucked, but what's done is done".
And to be clear, no, I'm not happy nor satisfied with "leaving it to mods", because while having a theoretical limit of six can easily be scaled back and rebalanced for a smaller party or even a solo game (as, you know, the previous BG games did) the opposite is not true: a game tuned around a max of four characters is going to feel TRIVIALLY easy played with six.