As mater-of- fact I had an PI running on 64-bit by “pasting” a centos rootfs on a open-suse kernel booting on u-boot and grub. Clever stuff the suse-boys are doing.
But another fact is i’m actually running 32 bit on a 64 bit odroud-c2 because it is faster - or to be more precise - have more headroom in memory.
Note running 64bit has it’s advantages if you are doing heavy calculations, shoveling data around it does not bring as much as much as you expect.