At Indiana University we requested through our CSM to have MathJax updated some time back, and also got a reply back that MathJax v3.x did not meet Instructure's requirements for internationalization (i18n). Instructure provided a rather ambitious list of languages that MathJax would need to support. This was due to MathJax's context menu, not the underlying accessibility plugin (the Speech Rule Engine (SRE)). The SRE has the same language support in MathJax 3.x and 4.x as it did in MathJax 2.7.7. It's the SRE that provides the braille output and speech text renderings of the MathML.
The MathJax development community was seeking funding to have the i18n features developed. Happily, they have recently received the funding via the Disability Resources and Educational Services (DRES) department at the University of Illinois Urbana-Champaign. Hopefully this work will alleviate Instructure's i18n concerns. I am not sure though, of the timeline. I hope to have an update on that in the near future.
Alternatively, it would be great if Instructure could provide a configuration variable for Canvas admins to choose which version. I imagine many universities would be quite content with the language support already in MathJax.
It would also be great if Instructure allowed Canvas admins to customize the MathJax config. Moodle does this. For example, there are useful config settings that have MathJax parse mhchem LaTeX macros if your chemistry dept. wants to display chemical formulae in Canvas pages and Moodle's site admins have the ability to set the config settings used by MathJax to enable it. You can see where Moodle documents this process here: Chemistry notation using mhchem - MoodleDocs
If Instructure does not allow for customization of it, perhaps we should work as a community to determine the best MathJax configuration and recommend it to Instructure. This is important as many of the sites I've found that are using MathJax 3.x have MathJax configured by default to hide the underlying MathML. Unfortunately that makes tools like the older MathPlayer or the newer MathCAT+NVDA combo not work without a student knowing how to manually change the MathJax settings. On those sites, JAWS, VoiceOver, MathPlayer, and MathCAT simply skip right over the math.