Ps. I think a cool potential solution would be a way to summon a 5th companion during parts of the story where it would make sense for one of the characters at camp to come along. The character then attaches to one of the party members as a temporary summon under our control.
This could work with an item like a Horn of companion summoning. Or perhaps just a dialogue prompt where the party can choose to invite a companion to appear, at points where it makes sense for them to do so. Either way you'd have an option to decline, if for some reason you didn't want a character around (for approval reasons or whatever) but at least that approach would have them along for the ride in some capacity.
There's already a part of the game where a certain companion joins you just like that if you ask them to, might be a lot of work to implement it for all of them?
Considering the mods already out adding a 5th slot to MP games that can only be used by a companion character might be easier?
