Since 64 bits can serve /many/ use cases and also matches modern machine words I could see there being either two drivers (one with 64 bit native words and the

Since 64 bits can serve /many/ use cases and also matches modern machine words I could see there being either two drivers (one with 64 bit native words and the other with full sized ones) or even a fancier driver that uses different ASM bits to just leave half the word all 0s and ignored. The on-disk format could even remain the same; it wouldn't really matter except for lots of small files and those are already so horrid that ZFS might have some other way of handling them. (Like treating /all/ small file names and data as part of a larger directory file or something.)