Re: FOX Shared Universe
With the FF reboot being development right now, I don't see why it would be impossible.
Its not like they are integrating the FF world featuring Jessica Alba and the actors we saw in FF/FFROTSS into the world of the X-Men. The world of Fantastic Four hasn't been established yet since its being rebooted right now.
X-MEN: DAYS OF FUTURE PAST
The future of X-Men's original trilogy cast begins this May!
Hugh Jackman - Halle Berry - Ian McKellen - Patrick Stewart
Anna Paquin - Shawn Ashmore - Daniel Cudmore - Ellen Page