Bear in mind that avionics software as a whole is a broad category that includes everything from fly-by-wire flight controls to the onboard entertainment system. Each system is classified under an appropriate Software Level as specified in DO-178C:

https://en.wikipedia.org/wiki/DO-178C#Software_level

The OMF system described in the video is Level E, meaning it's failure would have no safety impact on the aircraft. This gives us greater latitude in choice of software solutions. The higher levels, however, have strict requirements regarding latency and memory management that would automatically preclude the use of Clojure or any language with garbage collection.

So, as always, it's selecting the right tool for the job.