Definitely! But this series has made a lot of bad choices in the past, so if they want to set in the past, good luck to them.
This has to be the most bumpy film series ever released for its sheer amount of missed opportunities and bad timing. I'm gonna make a list for fun/theropy:
X-Men: Establishes the series for a great sequel, seemingly kills off Sabertooth and squanders all potential story-lines.
X2: Pretty much perfectly builds on the story and plants seeds for another great sequel.
The Last Stand: Kills off several important characters, "cures" others, forgets about Nightcrawler comepletely, and squanders the Phoenix and Gifted stories. It does however introduce some interesting characters and leaves a number of teasing questions to resolved in future installments (Neither of these amount to anything).
XO: Wolverine: Soullessly retreads Logan's origin and adds nothing of substance to the character. Plants seeds for a sequel in Japan as well as potential Deadpool, Gambit and First Class spin-offs.
First Class: Bears no resemblance to the First Class teased in the preceding film. Effectively ditches TLS and XOW, contradicting them in several places and damaging continuity. Sets up a great new cast for sequels.
The Wolverine: Another film teased in XOW that largely shuns XOW. Instead of being direct sequel, it takes place in the present day. Unlike First Class however, this film embraces TLS, builds on it, and even goes some way to redeem it. The film ends with a suggested Logan/Yukio sequel and a deleted scene teases the classic costumeid-credit sequence. Mid-credit sequence skips right over that and instead sets up the next movie.
Days Of Future Past: Makes for a compelling sequel to both TLS and First Class. While the present day timeline is effecively restored, a good number of the First Class characters are viciously axed, leaving this timeline a little worse off. Writes a lot of previous films off, most notably The Wolverine as it was only a year old at the time. It perfectly sets up potential OT or FC sequels, and hints at a Logan and Mystique story.
etc etc
Funny that all the films teased in Origins will likely come to pass, but all will disassociate themselves from it.