Hmmm - smartphone mining would be a splendid feature . . . any idea how much more efficient a GPU vs a CPU setup would be - say based on the cost of purchase of most efficient GPU vs CPU setup + 1 year of electric fees. If the GPU setup was 2X more efficient, I could live with that for the advantage of a wide variety of mining equipment (phones, game consoles etc), but if it was 10X, not so workable.
I have very limited data. A GTX980 with a TDP of around 160W was 5x faster than an i7-4790K with a TDP of around 80W. So the GPU appears to be between 2x and 3x more efficient in this case.
But since Cuckoo Cycle is memory bound, neither CPU nor GPU is going to be near their TDP.
So we really need to bench it with power measuring tools, which I'm lacking...