The problem here is that ARM & x86 have very different memory models, not that the ISA itself is a big issue. Re-compiling for ARM is super easy, yes absolutely. Making sure you don't have any latent thread-safety bugs that happened to be OK because it was on x86 that are now bugs on ARM? That's a lot harder, and it only takes a couple of those to potentially wipe out any savings that were potentially had, as they are in the class of bugs that's particularly hard to track down.