FSX has some fantastic products coming out in the future. Not just from Captain Sim, but a lot of other developers too. So I believe it has quite a bit of life left FSX. Now that modern computers can finally give FSX the performance we want/require for FSX AND at a cheap enough price for many to be able to purchase them, it looking quite good right now.

Although I can't answer for Captain Sim and what their plans for the future are, especially towards X-Plane, but with the imminent release of the 737-100/200 and Expansion Packs, the 777-200 and Expansion Packs AND the redoing 757 (v5.0) and 767 (v2.0) being mentioned, the workload by the small team required for those, I can see many resources left for development for products for X-Plane.

I could be wrong. So unless Captain Sim say something, my guess is as good as any other guess! ;)