mrfuji3,
Oh yes, with Larian at the helm, anything is possible.
On one hand, this
thread states that they are neither demons nor devils, just creatures from Lower Planes, and besides they are NE. So technically Mizora shouldn't be a succubus, at least from 5e perspective. However, I don't know if it eliminates the possibility for her to be cuarterona succubus or even less, with the majority of her infernal ancestry coming from devils.
On the other hand, Raphael also seems to be a shapeshifter. Chances are, it might be the approach "invented" by Larian.
Personally, I'm also not convinced that Wyll had any kind of affair with her. Maybe I didn't long rest enough, but Wyll only speaks about her in purely "business" terms, and never mentions anything else.
