Yes... something like that. I think I wrote up some notes somewhere, but the best summary is in this Mongol thread: Mongols in 5th which I pasted in the suggested summary of what a "magus-level" shaman would be like, but I think I was asked not to be too detailed so as to not make it canonical and also to leave room for interpretation.
At one stage I considered having them built off "Spirit Votary" as the core but can't recall why i abandoned that, it seemed easier to just mix in some existing powers and abilities. One of the issues with that though would have been the need to have multiple books to make the tradition work or otherwise reprint large parts of HMRE, which was against line policy as, to be fair, people wanted new material when they bought a supplement, not just a whole lot of reprinted material.
Given we already had sahir as the "rival tradition" ie near Hermetic power level tradition for the book tCatC, there wasn't really room for another one although I think if you did do a Mythic Steppe Saga, then "magus-level" Mongol shamans are a reasonable idea.
An Open Ars Magica ruleset would go some way to offsetting the reprinting concern if it followed the "mechanics are open, campaign content is copyright" precedents...