The gameplay would be broken as it is now if there were 6 party members. Larian would have to completely remake every single aspect of the gameplay to accomodate 6 party members.
No, it wouldn't. And no, they wouldn't, either. Also, all this "concern trolling" about upsetting the current balance is laughable, as there's very little balance to begin with and all the encounters currently available are basically an open work in progress that will require more tuning for months to come regardless of possible party expansions.
Even the terrain does not accomodate more than 4 at times. All the fights would be severely broken and ridiculously easy with 6.
Another made up and entirely baseless claim, that among other things ignore that managing a party of six wouldn't even be this "crazy experimental idea" but a standard countless games already road-tested for years.
It is an enormous task to ask Larian to rework the game to have 6 party members.
No, it's not. Modders can already have a six-men party working now, and that's without even a mere fraction of the resources, manpower and access to the game's code Larian would have in its favor. It would require a rework of the controls, on the other hand. Which it does anyway, because the current ones are the stuff nightmares are made of.