It would be very, very cool if you could use characters in your legacy as companions. Jedi, Sith, Troopers and Imperial agents would only be able to assist characters of the same faction. Smuglers and BountyHunters would be able to assist both due to their slightly more ambiguous loyalties.
There would obviously have to be limitations, such as auto-scaling the character's stats to your level. However, I think it would be an interesting mechanic and actually allocate a purpose to the legacy system beyond purchasing buffs.