george torrey wrote:
I'm curious if there's been any sort of hint or dropped clues about the likelihood of an Inhumans volume.

The fact that the Inhumans back-up stories from Thor -- prime Kirby material, as you point out -- have not been included in the Thor Masterworks is IMNSHO a pretty large hint that *something* is being planned.

Whether that something is a Masterworks or an Omnibus, time will tell!