The wg should (imho) explicitly state if the issue is getting rid of MD5 or getting rid of MD5 at the same time as a whole bunch of other things are done. That will probably make this process go a whole lot easier.
David has posted the set of requirements that a solution needs to meet. Beyond those, the WG can also take into account other desirable security characteristics in making a determination.
However, in doing so, I would warn against feature creep. RADIUS has succeeded largely because of its simplicity and modest footprint. So the goal is to address the crypto-agility issue with a minimum of unrelated changes.
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