I guess I should have said that I would absolutely love to go FF in the future. I was thinking about going FF (with the original 5D) when the 5D2 came out but when the 5D classic didn't drop at all in price when the new body came out I couldn't justify spending the extra $900 over and above the cost of the 50D to go FF. Seeing as this is probably a lens I would keep for a while into the foreseeable future I would want something that would be compatible with both bodies (if I end up with a crop and a FF) or with FF if I eventually have 2 FF bodies. This was the only thing I regretted about the 10-22 purchase, and if I am going to spend an extra $700 over the cost of what I can sell my 10-22 for right now I would probably choose not to buy something that isn't fully compatible with a FF body (just keeping in mind future considerations) without having to crop or do heavy PP work to control vignetting (11-16).
So, that being said, even if we left out the idea of getting rid of the 10-22 for now (at least until I do go FF), would this be a good addition to my gear (I would probably ditch the 17-40 even if I keep the 10-22, so I have that as a source of income toward the 16-35)