This was something that popped into my mind while I was thinking about CPU Only Alt-coins. Would it be possible to have an ARM-based coin? That is, a coin that could only be mined on ARM devices (iPhone, Android device, etc. )?
You just need to find a hashing algorithm which is more cost efficient on an ARM CPU, I found this answer to a similar question which should point you in the right direction :) https://security.stackexchange.com/questions/29941/how-does-processor-architecture-affect-password-hashing-speed