Year-over-year improvement is what matters
I just heard that a group of people is working on a CMMi-like framework for Agile Product Management. And of course there's the Agile Maturity Model. And various surveys to assess Agility.
"Maturity" and "agility" are the wrong things to measure.
Level doesn't matter.
Results matter. Year-over-year improvement matters.
I've seen plenty of companies that assessed at some vaunted level, but still produce crappy results and still grind engagement and creativity out of their employees.
"Maturity" and "Agility" are proxy measures have the same risks as all measures: they focus attention on the wrong things and often drive behavior that's counter-productive.
Focus on doing better every day. Practices help you do that. Removing organizational impediments helps you do that. Improving skills does that. Improving the quality of management does that. Improving team capability does that.