I think the title speaks for itself. It could promote people playing more than dps and leveling tanks and heals for use in their warband. If not maybe offer default heroes to help or w/e.
Then if in a group with friends you can choose what toon from the leaders warband to pull in or something to fill out the party.
Just an idea.
Its possible but I think it would add a lot of extra load to the back end as it would need to draw the characters race and item ids from your account much like the key ring.
I’ve always hoped we’d get something like this, even if we could just pick one alt as a follower, it keeps its name, gear and spec, but just follows you around helping out and soaking experience from your kills. Much better than those random followers we had in previous expansions.
Holly Longdale already has the gears turning in her head with this idea:
If it’s possible while Warbands has some potential. 
Although I would adore drama interactions if the current (or planned) followers encounter specific bosses, ruins, or quests.
edit: Such as a follower is afraid of snakes and wants to avoid the optional boss for my crazy idea. 
Thank you so much for posting that!