Re: 'X-men: DOFP' Official CAST Thread (announcements and discussion)
Bryan could still do other movies between X-men sequels, specially with Fox releasing them with a 3 years gap.
If they would have signed Singer before the Superman offer, WB would have choosen another director or wait for Singer to release it later.
And on the actual scenario where Ratner did X3, if Fox would have called Bryan some years later offering him the fourth installement, I think Bryan would have accepted.
X4 didnt have to come out on 2009 at all, maybe on 2010, so that would have given Bryan some time to do another proyect, like Valkiria, for example.
Next Big X-Men Crossover
* 2017- X-Men: Age of Apocalypse
Edit: Forget about 2017:
Official announcement -> X-MEN: APOCALYPSE - MAY 27, 2016!!!!