The creator of Linux has commented about the relevance of 32-bit architecture
Linus Torvalds has admitted, in a rather odd context, that the 32-bit platform has become less important than the 64-bit one.A kernel developer sent a pull request to fix a problem that only applied to 32-bit kernels. Linus' answer was that it's too late to be included in the 3.12 first release and that it's not all that important anyway.
“Yeah, I think the circumstances have changed. 32-bit is less important, and iget() is much less critical than it used to be (all *normal* inode lookups are through the direct dentry pointer).”
“Sure, ARM is a few years away from 64-bit being common, but it's happening. And I suspect even 32-bit ARM doesn't have the annoying issues that x86-32 had with 64-bit values (namely using up a lot of the register space),” said Linus Torvalds.
Well, there you have it. Even if it's an admission of something that most of the developers already believe, we have to keep in mind that a lot of people are still running 32-bit machines and it will be a long time before they get phased out.