According to Collider, it seems like The Inhumans are apart of Marvel's next exploration of their expanding cosmic universe. The studio has a script by Joe Robert Cole, who is apart of Marvel's screenwriting program (Guardians' co-writer Nicole Perlman was also apart of that program). The situation sounds very similar to when Guardians landed in the lap of James Gunn, after the script was developed in-house at Marvel. Also, Doctor Strange went-out to filmmakers before Scott Derrickson was announced as it's director, and Jon Spaihts (Prometheus) was hired to do a page-one rewrite of the script. We could see another complete overhaul on the existing material. Apparently, the film/script is going out to filmmakers and might need a strong visionary to further develop it.
We previously heard that Marvel was developing the property for a feature-film, but a writer was never named. The last word was, Inhumans was one of three candidates competing for a release spot (Guardians and Black Panther being the other two), which Guardians of The Galaxy would ultimately get. The project was being described as Game of Thrones meets X-Men, as superpowered royal families fight over galactic thrones. Inhumans is such an interesting property, as we've heard this could be a way Marvel is able to develop their own type of "mutants" (owned by Fox) within the MCU.
Recently, Vin Diesel teased fans that he could be "Inhuman" for Marvel. This could be another misdirection by Diesel, or a way to push his own agenda to gain another role at Marvel. Many believe this might mean we might see Vin as the voice of Groot and the body of king of the Inhumans, Black Bolt. Black Bolt's voice is beyond destructive, which means he doesn't speak and would allow Diesel to play two roles within the cosmic universe.
Could we see another creative/unexpected voice like Gunn spearheading our cinematic introduction to The Inhumans? I'd love to see someone unique like Ben Wheatly (A Field In England, Sightseers, High-Rise, Kill List), who I've been dying to see show-up on one of Marvel's director wish-lists. Given that Marvel went with someone a bit more rebellious like Gunn, someone like Ben (known for bizarre/dramatic projects) might be another winning combo. Ben is currently shooting his thriller High-Rise with Loki himself Tom Hiddleston, and has recently directed an episode of Doctor Who. He also wrote his darker films A Field In England and Kill List.