I'd approach that kind of decision VERY carefully. While Maya definitely has its merits and is a welcome addition to any pipeline, Max is still a pretty big powerhouse in gaming department. Some inside numbers show that it is, by FAR, the most used DCC to export stuff into Unreal. Going point to point:
"It’s difficult for us to find experienced (and even relatively inexperienced) candidates that have a good level of familiarity with 3DS Max (Part of this I think is due to the geography as we’re located in relatively small and somewhat isolated pocket of the industry.)." - True, and the best ones are already employed in large studios and pipelines. Just recently a new founded studio had trouble finding Max artists in NY area. The competition to grab Max artists is getting bigger and I blame the lack of them in two fold - the education material favors Maya big time and the marketing also tends to lean towards Maya too. It also does not help that the Viz market is getting hotter and hotter (and generally pays more for entry level artists than gaming industry does).
"As a result of the above point, we often end up hiring candidates that have strong Maya backgrounds, but little experience with 3DS Max. This of course increases our onboarding costs significantly." I'm sure I'm not the only one here that finds that teaching a Maya artist how to use Max is easier than the other way around. And (as Xerges said) a Max artist is prone to spill his talent on other areas, helping productivity and delivering faster when deadlocks are found. My hint? Train them to use Max and see what comes as result.
"Similarly, many of the outsourcers that we work with are not well equipped to efficiently interact with a studio that principally relies on 3DS Max for its rigging and animation pipeline." We are! Get in touch with us if you need help! We do everything from modeling, to rigging to animation to final frames. We are small studio in Brazil but ready to tackle and help any Max pipeline deliver!
"We miss out on a lot of really cool, non-Autodesk tools that are either Maya exclusive or just better supported on Maya (Red9’s tools, Epic’s A.R.T tool set and Fabric Engine come to mind)." That I can't help you with, but there are plenty of awesome tools made in max and for max from several guys and companies all around. Regarding Epic's A.R.T. isn't this kinda of a "biped" version for Maya? And Fabric Engine it's already on its final Beta for Max http://fabricengine.com/fabric-3ds-max-final-beta-come-give-spin/
"There’s also a perception at the studio that the skills and knowledge sets of our TAs and animators are falling behind industry trends, leaving our team members out of sync with the current and future needs of the broader industry. Admittedly this last point is a bit self-serving. However ultimately, I do believe that the transition to Maya represents a “rising tide lifts all boats” scenario in that these sorts investments in personnel generally provide a favorable a ROI for companies." This perception is just wrong and prone to change.
Anyway, make this move after some serious thought! Losing productivity equals dying in a competitive field as games.