Doing this in the three kingdoms style would probably be the best case scenario. However, I haven't looked, but I assume there will be a medieval 2 mod out there that meets some of these requirements.
On a related note, I feel that the Arthurian Legend theme is drastically under-represented in modern games. So much potential there that hasn't really been touched on in this medium for some reason.
I agree that Three Kingdoms was surprisingly good, but that got abandoned by CA really quickly. Didn't they cancel some major DLC and all updates for that game?
I doubt they will follow that sort of formula since they appeared to lose faith in it so quickly.
Ultimately, if they go with the more "realistic" style, then I see no reason not to just stick with Medieval 2.