yum in fedora 9 has an option to do the same stuff which basearchonly was intended for.(Its even on by default) So there is no reason to ship/maintain the plugin anymore. We should drop it from the yum-utils package and make yum obsolete it (to make sure it gets deleted on upgrades).
yum-utils-1.1.x also works with older version of yum that is currently in F9, so it is to early to drop it, but a obsolete in yum might be a good idea.
I've added the obsolete to the yum package upstream and into rawhide.