Fox wont let the X-Men rights go, thats for sure.
Will be interesting to see how far they go with the two current casts.
They could easily keep moving with the whole cast or part of it... and adding new characters/actors will let them continue without the need to have all the actors that started the series, either X1, or FC1.
I wonder how much time it will take for Fox to release next spin-off.
If they really want to have a similar take as Marvel Studios, releasing not only team movies..... I think we'll get a new spin-off sooner rather than later.
DOFP will be huge, so that will give them the confidence to make the x-men movie universe even bigger, giving the greenlight to the second spin-off after Wolverine. What will it be?...
we'll have to wait one year or so I guess
Next Big X-Men Crossover
* 2017- X-Men: Age of Apocalypse
Edit: Forget about 2017:
Official announcement -> X-MEN: APOCALYPSE - MAY 27, 2016!!!!