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.
Anyone who complains about 'balancing issues' when an idea is presented is a selfish moron. It's like the argument "It would take too much time to impliment" from people with no coding experience and surmounts to "I'm happy with it so why should I accomodate your idea". How something is balance is a task for the devs to consider not the playerbase and is a completely irrelivant criticism to make. Anything can be balanced if done right and is done after the fact, not in spite of it.
You have made a lot of really solid points and I agree with all of them. Especially the idea about giving 'party experience' instead of 'individual experience'
Something I'd like to add is that a large issue, due to Larians current creative decisions, is that every single fight is mapped out and planned. Nothing is really 'randomised' and thus you end up with a pretty static game after multiple playthroughs due to the lack of 'living world' elements. I've made these points in the 2 suggestions in my sig. Random encounters,respawning / repopulating enemies, coding dynamic encounters that increase/decrease the enemy numbers in response to party size. (For those that want to whine about cannon, it'd be easy enough to add 'priority units', like commanders, that carry a warhorne they can blow to summon reinforcements) are all elements I feel like Larian need to include