I'm curious. The Terris supplement had a history of the people group, and we know that the Final Empire hasn't always been under the plantation system (It's, like, only 300 years old according to Elend's book, right), so I wonder what other systems the regional Skaa would have been under?
My guess is either full-blown slavery, or a very strict caste system. Seeing as the plantation is a step up, and in it nobles are basically leasing skaa from the Lord Ruler, both seem strong possibilities (depending if you think things are getting "better" or "worse" over time).
What is interesting to me is, how do City Skaa fit into the system? The Tradesmen morph into an almost full blown Middle Class fairly quickly once the Final Empire ends, and they seem to have far more freedom than the Plantation Skaa... how does this work? If the Lord Ruler leases the Plantation Skaa to the Nobles, are the City Skaa "unleased"? Anyway, I look forward to Tin and Ash and how you make all of this work.