As with pretty much every decision Jim Hackett has made since becoming the interim AD, this all seems about right.
It's been time to retire #21 for quite some time now, but the "legends" experiment probably delayed that eventuality, although we did get a chance to honor Desmond before the ND game in 2011 which was cool.
As for the rest...11, 47, 48, 87 and 98, those numbers will forever be remembered by this current generation of Michigan fans for the most recent players to wear them, and not the legends they were meant to represent...which is a shame.