Yowzas! That sounds pretty awesome. A Game of Thrones style Inhumans film where the Inhumans become MCU's "X-Men"? Sweet.
Why does this work? First off anything GOT style with warring powerful figures realpolitiking sounds like a fantastic new twist for the MCU. Second, since Marvel/Disney does not have access to mutants they can use the Inhumans as a mutant substitute. That dynamic between the mainstream heroes (Avengers) and the mutants (now Inhumans filling a similar role) has always been an important aspect of the comics. This is finally a way of brining it to the big screen without access to the mutants and X-Men. Let Fox do whatever the hell they want and continually try new inventive concepts on the big screen.
This sounds like a Phase Three winner to me.