Possibly off-topic, but the Reachmen could be related and would also be a cool addition even if in dlc/ep. No game citation there either though...
http://www.uesp.net/wiki/Lore:Western_Reach
Could be interresting to encounter the Witchmen of High Rock on the western border, and it might be a connection between them and the Witch-Warriors of Skyrim.
My own speculation on the Witch-Warriors:
I would guess they are a clan(or several) with their own culture, possibly with connections to the Glenmoril Witches.
They have either passed the art of "rune-enhancing"(with a lack of a better word. See http://www.uesp.net/wiki/Morrowind:Nordic) weapons, or they trade with merchants.
They practice magic that is possibly outlawed by either the College of Whispers, the Synod or the Empire.
They might have a similar sosial standing as the Ashlanders in Morrowind, being distrusted by most people.
If it is a Witch-Warrior clan I hope you can be adopted in, but you have to prove yourself.
They might teach you how to rune-enhance weapons(like a perk, but not one that is chosen on lvl up).
Anyone else have thoughts on the topic?