https://www.yahoo.com/news/x-men-mov...180502331.html
So the rumor is Fox wants IN with Disney/Marvel. Just like Sony worked out a deal with Disney, now Fox wants to do the same thing.
This would be an excellent idea. At the end of X-Men Apocalypse, a cool new team of X-Men have formed. They just need a new DIRECTOR (perhaps a new screenwriter as well), and better marketing, but an affiliation with Marvel could help with that all.
But really I think both companies though they didn't actively talk about it, left the door open for something like this.
In DOFP, we met Quicksilver and his little sister (possibly Lorna Dane). Wanda was alluded to be not shown. In Avengers two Quicksilver and the Scarlet Witch were introduced, but Quicksilver was killed off. And the twins parents were never shown. Both studios left things open to rework things to unite Magneto's family, if the rights were worked out . And in the comics the Scarlet Witch and Quicksilver were implied not to be Magneto's children, but this was never proven.
I do think Fox is giving serious consideration to working out something with Marvel, as a boost to the Fox cinematic universe. I think in the not too distant future we'll see mutants in the MCU, when Fox and Marvel work out their sharing deal.