Now, it may be a fit of crazyness on my part, but it would be nice if we had access to a special kind of hireling that represents a character who is a companion of the main character. It would work like a custom hireling, but maybe the player can control it for a little while (say, up to 1 minute per rest) and the main character would meanwhile behave like a hireling.
They would be created in special character slots purchased with TP and level earning XP (or be bound to a character and be always of this character's rank and level). They wouldn't be hired (that is, you don't have to pay them in advance to join you in a quest), but share the loot (there would be less treasure for the main character, and the player must equip them with equipment the main character has in its inventory, although a Companion's equipment can't be sold or given to the main character, just destroyed, representing the companion selling it)
The way to interact with them outside dungeons wouldn't be through Hireling vendors, but "leaving a message" in a tavern for them with a Barkeep.
Now, any comment that doesn't say just "that's a crazy idea"?