Marvel 100% tried to replace the X-Men with Inhumans, and it failed miserably. What started out as a movie idea, to have Inhumans be the X-Men of the MCU, turned into a low budget tv series. When Inhumans comics sales also failed hard, they gave up and decided to bring back Jean, Logan, Professor X. Now that they'll have the X-Men movie rights back, I'm guessing you'll see Uncanny X-Men relaunched with an A-List cast, creative team, and they'll be featured prominently in Marvel marketing, even if the MCU and X-verse remain separate.