The empire banned it.
Khajiit and Argonians are a bit far away to be a constant source.
I see the old style slavery in Skyrim.
Convicts and vanquished enemies, hobbled and used as manual labour for chieftains and or tribes.
Also a second class system at best, Dunmer are likely to be treated as stock for this.
As if you read the real Berenziah you see that noble Nords have a history of treating others as inferior.
I agree. Basically, slavery is more prominent in the south and east of Tamriel, where both beast races who are ensalved as well as those who wish to enslave them are plentiful. In the north, in Skyrim, I would like to see a caste system, perhaps with some minor suggestions of serfdom on occasions (but not too much, because I thoroughly hate the concept). Lorewise, I believe it'd be the most appropriate form of segregation/social distinction between different groups in Skyrim.
it has been played out. it doesn't matter if the culture is different. slavery in SK will mean the same character topics that already appeared in MW: slaver is bad/ slavery is good. you help slaves escape/ you catch slaves. we did all that in MW. why do it again. besides, the hot topic in SK is civil war, not the ethics of slavery. it might exist but it isn't going to be a big deal.
I disagree. Although I don't think slavery will be as prominent as with Morrowind (for obvious reasons), I believe that some minor cases of slavery should exist to spice up the game world.
As for the argument that it's played out, poppycock. There's a civil war going on; mix that up with slavery and you've got some amazing potential for moral conundrums. Imagine - a rebel Nord town captures a small Nord pro-Imperial patrol; some may clamour for them to be enslaved, hating them for their loyalty to their empire and regarding them as dogs. Others may recognise the kinship through their differences, and petition instead for them merely to be imprisoned and tried. Ultimately, the decision rests upon you, with multiple possible outcomes. Obviously, it'll be tough to decide and you may feel terrible, but the game will be better for it. Anyway, this shows how slavery isn't just a concept of slaver bad slave victim as you suggest; to reduce such a notorious and important institution into black and white is silly to say the least.
TL;DR I'd say there's still a lot of juice left in that motif to power up some tough choices, especially when you mix it up with the civil war (which itself should be morally challenging).