Re: 'Days Of Future Past' BOX-OFFICE worldwide prediction
If X3 made almost 500m worldwide back in 2006, 8 years later this event movie, on 3D and with actors from both series will make much more than that, thats for sure.
And if the movie ends being really epic and intense, word of mouth will be a key factor to make it a great success.
None of us can know how far will it go, but less than 600m seems kind of unlikely, taking into account all factors.
Next Big X-Men Crossover
* 2017- X-Men: Age of Apocalypse
Edit: Forget about 2017:
Official announcement -> X-MEN: APOCALYPSE - MAY 27, 2016!!!!