Just popping in to say that what eventually fixed this issue for me was setting ffxivboot64 to compatibility mode for Windows 7 and launching the game that way. Game worked fine yesterday, today nothing but DX11 errors. I spent over two hours crawling Google and these technical forums, trying dozens upon dozens of fixes and work arounds. Even tried a completely fresh install on a different drive and had no luck. Eventually I decided to fallback to the old way of fixing things: tell it to run in compatibility mode. And I'll be damned if it didn't fix the DX11 crashes. Played for four straight hours, ran a few duties, did everything I could think of to "stress" the game and no crashes. I have no idea if it'll work for anyone else (if you're running a 32-bit version of Windows, try using the regular ffxivboot instead of the ffxivboot64), but I figured I could at least post my own solution here to add to the hundreds of other suggestions that worked for other people.

Cheers.