Does it really make sense?
If the problem was that the instruction set was outdated that would make sense. But if we keep talkig about 34 vs 64 bit the question is how many apps actually need 64 bits? I guess that most of the smartphones don't even have enough memory to serve apps that would take advantage of the difference and that won't change for a while, I mean that a smartphone may have more than 4 GB of RAM, but it could not allow a single app to use all the memory.