After all, the movie already featured a returning X-Men team, a young X-Men group, Wolverine, William Styker, plus Apocalypse and his horsemen.
Even though the X-Men were eventually successful in changing the future, it appears Trask was close to returning earlier this summer in X-Men: Apocalypse.
Trask was a good addition to Days of Future Past, but it is hard to imagine him being included into Apocalypse as well.
Trask had a prominent role to play in the movie, with his Sentinel program taking off to eliminate mutants forever.