Do you ever boot your machine only into 32-bit mode? Most UEFI firmware I've seen is launching /EFI/BOOT/BOOTX64.EFI, which means your bootloader is in long mode even if you then switch back to 32-bit mode (and UEFI is likely already there). I don't know if emulating a traditional bios avoids this or not, never thought about it. But I'd take a guess that the vast majority of people are passing through long mode and then back again if they installed a 32-bit OS.

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.