Because Padomaic and Daedric aren't synonyms, they just tend to correlate. Heck, Lorkhan could be considered a Padomaic Aedra, so an Anuic Daedra isn't outside the realm of possibility.
Yup. Meridia could be one. Daughter of the Sun.
http://www.imperial-library.info/obscure_text/census_daedra.shtml
The Mnemnoli seems to be.
http://www.imperial-library.info/obscure_text/vehk_teaching.shtml
I would feel cheated if none of this really happened. I think it's exciting that there is a new daedric prince and a new demi prince.
Well it's not like that. You don't become a Demi-Prince or any of that seriously inconsistent stuff with arbitrarily assigned levels of power. All magic is symbolic, so if you walk like Sheogorath and you talk like Sheogorath, then you are Sheogorath as it's not the person that matters but their role. The role gives them their power to enact it.
http://www.imperial-library.info/dfbooks/b055_lightdark.shtml
When it comes to power by imitation that should atleast get you going in the right direction.
The Towers, Tiber Septim and the Tribunal are other examples.