Full-frame at APS-C prices would be great. It would lose one of the perks of APS-C: crop factor. Getting 450mm out of a 70-300mm lens is nice.

edit: since it's apparently not clear and I'm getting downvoted for sharing how this benefits a harmless personal preference, I will emphasize that I'm speaking to my needs. The 70-300 lens is what I use, not some abstract construct meant to represent all purposes.

The crop factor is generally a perk for people who shoot at the ranges I shoot at even if it comes with compromises for other needs.