Let's turn this around. You've said that you want to be able to play solo (with something like a lone wolf mode right?); how do you think such a mode should be implemented in BG3? -Increasing experience gain will have significant problems at the level cap, true. -5e doesn't have "skill points on level up", so BG3 can't simply give characters double the skill points. -Doubling the ability score modifiers (e.g., Con of 14 gives +4 instead of +2), the proficiency bonus, and/or HP won't scale well with level because power in D&D is heavily tied to class features/spell level. Even getting an additional full action (and bonus action) isn't sufficient, for this reason. Unless you play a fighter/barbarian I suppose...then it may work. -Larian could adjust all encounters for a Lone Wolf playthrough, but these seems like a LOT of work, and possibly require the player to commit to that mode for the entire game.
I'm honestly curious what your thoughts are on this. Because possibly, what will work for a party size <4, could potentially be inversed for a party size >4.