Full Idea
Maybe conceivability could be understood as a priori coherence, which implies possibility.
Gist of Idea
If conceivability is a priori coherence, that implies possibility
Source
Tuomas E. Tahko (The Epistemology of Essence (draft) [2013], 3.2)
A Reaction
I'm not quite sure why 'a priori' has to be there. Assessing conceivability just is assessing coherence. That couches it as a rational activity, rather than as a purely imaginary one. Trying to conceive a square circle isn't just daydreaming.