Naw, the Hero of Kvatch is still the prisoner archetype and becomes Sheogorath via mantle-ing.Sounds cool, though was not something like that also tried in Oblivion?
Even just bog-standard prisoners have extreme importance in the cosmology.
The MC here would be a literal who. Who just happens to know the prisoner. Either as a prison guard or a former associate or whatever.
Wrong place, wrong time, but determined as fucking hell. Everything they do is because of their own merit. No prophecy. No destiny. As well as having weird parallels to Vivec, and eventually achieves CHIM like him. He can be any race though. Doesn't need to be dunmer, and as a point, should have no default race or gender like in Morrowind and Skyrim. Where it's Dunmer and Nord respectively.
"Your destiny is your own. The dream is yours. Come what may. You will face it all." Being the arc words.