I'm not saying remove the possibility of 32-bit userspace and nor are, it seems, freebsd. I am saying don't bother with a 32-bit kernel. Otherwise you're limited to a 4GB address space and hacks like PAE. No harm in running 32-bit binaries if you want and, I think Solaris actually left userspace as 32-bit only even on their 64-bit OS, unless the application really benefited from a 64-bit setup. Not sure what they do now, been a while since I used it.
It's arguable ASLR only works well in a 64-bit mode, as well.
No, but I'm not everyone.
Or let me put it this way: I don't know the motivation for why the things work like they do. It's entirely possible there is no good reason at all. Or maybe there is? Either way, I wouldn't assume anything so quickly.
Are you sure it's "everyone"? No doubt it's "overwhelming majority", but that's not the same, and "everyone" is a lot of people.
As I understand how this works, the compatibility is perhaps slightly inconvenient to a small group of developers, but not that inconvenient and generally relatively cheap. So why not have and keep it?
ARM has a lot less history than x86. Yes, it goes back to 1985 in the BBC Micro, but didn't really see serious usage as a "generic platform" until the late 90s/early 2000s.