Of course what comes to my mind is a more graceful multiarch LiveUSB than current methods with multiple rootfs images. To contradict an earlier comment, that is an area that I think end-users could enjoy as much as developers. Of course getting a single LiveUSB partition to boot nicely/robustly on all the various arches is probably a nightmare task (or at least with recent rather than future hardware). But I'd like to see my rootfs with all my personal data be a microSDHC on my keychain that just docks with whatever phone/tablet/netbook/desktop/server I happen to want to deal with at the moment... (at least as a utility option). But yes, that requires the /usr/bin/ARCH/ complication as well.