I will put the rp considerations aside, since this is something which the characters can handle ingame however they like.
I do not like the idea of some item representing a slave (and everything in your inventory would be an item). That is quite unimmersive, and I would consider it a step back in the development of Illarion. HOWEVER! I do, of course, have a better alternative.
As some of you may know, I am working on a pet system. It has already been asked (by a player of a certain Cadomyrian noble) if this could also be used as a slave system. I think that this could be done with really not so much effort once I am done with my pets. Then, the slave would actually follow you around! Making them work should also be possible with some moderate effort.