While Sony Pictures and Marvel Studios may have mended fences, it's no secret that the relationship between Marvel and Fox remains contentious. X-Men: Days of Future Past and Avengers: Age of Ultron proved that the two studios can reluctantly share certain characters that are not exclusively tied to Marvel's mutant race. However, Quicksilver's appearance in the MCU was ever so brief Spoilers:[and if rumors are to be believed, so is his sisters!] (Read more about this spoiler by CLICKING HERE). However, it appears that there's another character (or race in this case) that can be shared between the two studios; the Celestials - a group of the oldest and most powerful entities in the Marvel Universe that are directly or indirectly responsible for the creation of the Eternals, Deviants, mutants, Skrulls and Inhumans.
Though Apocalypse is the first mutant, he doesn't become the neigh-unstoppable force he's most commonly depicted as until he comes across Celestial technology. Here's Bryan Singer's hint at their appearance, you decide if you think the Celestials will appear in X-Men: Apocalypse.
"The way I describe him the most, the best, is he to me is the God of the Old Testament and all that comes with that. If there isn’t the order and the worship then I’ll open up the Earth and swallow you whole, and that was the God of the Old Testament. I started from there and when Oscar and I met we began discussing -- since he isn’t really God, he’s the first mutant perhaps, but he’s not God necessarily -- he’s imbued with certain unique powers. Some of them may or may not be from this Earth, we don’t know."
Celestial in Marvel's Guardians of the Galaxy.