I haven't checked for mods for this yet, but I think it would be a good addition to the main game. There was a lot of work on all the companions, but I don't use them for two main reasons: You don't seem to get xp unless you also hit the creatures at least once, and the companion commands are almost impossible to pull off. Sure, there's other problems with their AI, etc... but they'd be a whole lot more useful with two very simple changes.

Let companion kills still give you 75% experience (or maybe 50%). The more you kit out your companions, the more experience they steal from you. So instead, it's usually best to have them extremely weak, have them run in the middle of a group and play bullet sponge... over and over and over. Kind of takes away from the immersion. If you didn't have to worry about tagging each enemy in every encounter just to get the experience, you could actually use decent tactics in each encounter.

More importantly, have a bindable button for giving companion commands. The commands make for reasonably decent AI/tactics... if you didn't have to scan around to find your companion, get caught in a really slow scroll if they're close, then finally scroll over to finally give the attack command. Usually by that point, you're already mostly dead because this is in real time, or hiding behind cover so you can't give the attack command anyway. A one-button command would actually let us actually use the whole companion command system.

Two very simple fixes that would probably encourage a very large portion of the player base to actually use companions, or at least be happy with them.