With the new thrall limit coming in, it would be handy to have a useful way to dispose of thralls that leveled up poorly or are otherwise no longer needed. A useful disposal mechanic would also give maxed-limit clans a reason to keep breaking thralls and participating in that part of the game.
My immediate thought is human sacrifice to gods. Sacrifice and get a long lasting (24 hour?) “blessing” buff or a good consumable item. Effectiveness could scale to thrall level, sacrificing a level 20 would give a sizable increase over a level 1.
Second thought is simply a thrall vendor. Sell them for gold & silver, always needed for alc powder. Also scaleable and probably easier to implement. Yes, this would make us active slave traders.