I'd imagine it wouldn't take much more than just finding the menu sound files and replacing them. Doesn't sound too difficult, although I have no idea how to replace sound files besides those on stages lol. Surely there's a mod out there somewhere that has already gone ahead and done this?
EDIT: Forgot to say the whole point I was trying to get at lol. Yes, it'd be low on their list of priorities (if it
were a priority in the first place, which it probably isn't), but you could still easily get it for your own personal build by downloading a mod that very likely already exists.
EDIT2: I would check
this out. If it isn't already part of the build this guy is making (you can ask which files pertain to the menu sounds and ignore the rest of the build), you could probably request it since it would probably become a popular idea and easy addition.