The only problem I can see going with a Titan over a 1080 is that I'm not sure DCS will use it.
Now, a guy probably uses his system for more than DCS, I know I do, but for this sim specifically, I think the bigger issues are software (no specific VR coding) and CPU based (no multicore). I'm willing to bet that even with a new version of Rift (higher resolution), it wouldn't be an issue given most of us are running a DP of 1.6 or higher and a new Rift wouldn't require that.
I dunno, I've thought about buying a Titan myself, but I just can't see where the GPU is the bottleneck.
Either way, I hope you enjoy it, it'll be a killer card.