dumb question but are there any plans to add support for newer versions of ffmpeg? 
Yes, eventually, though it isn’t the highest priority right now.
FWIW, one related update in the next release is the addition of Opus support.
We have the same request because the current supported library means having to maintain two versions of ffmpeg.
Assuming the trouble isn’t enormous, would it perhaps be a good idea to add the option of using a non-approved library, with the caveat that users do so at their own risk i.e. that Audacity Team will not be held liable for loss of eyebrows, missing kittens and the like?
You can always use whatever version of FFmpeg you want and then use export using (external program)
I know this (mostly) works as I have been QA testing it for some recent bug-fixes.
WC
use export using (external program)
Thanking you Sir!
We never noticed this in the drop-down list and it works a treat.
If there were some thumbs-up smilies then you’d have a pair for sure.
Glad it worked for you - and thanks for reporting back 
Peter.
Finally !!!
Thank’s to developper to work on it 