Nintendo fixed the hole that made boot1 vulnerable in newer Wii's, and boot1 is a one time programmed thing that can't be changed so it can't be fixed (as far as we know now).
One thing I'm not sure about though is if everyone's Wii that can't install boot2 bootmii at the moment really doesn't have a vulnerable boot1. Is it possible that with all the extensive checking Team Twiizers went through to avoid bricking people it blocked more installs than possibly necessary? A friend of mine told me it wouldn't let him install to boot2 on his launch Wii, which struck me as a bit odd. So maybe it would be possible to at least extend compatibility to a limited amount of users that may not actually have a fixed boot1, but maybe something else that the current beta version didn't want to risk attempting an install with?
