After sitting on this for entirely too long (we were waiting to roll it out with some other related code, which hasn't happened), we have finally incorporated it into the existing system.
The system will not automatically assign the new MIME types to existing files--we didn't want to trigger a sudden, unexpected change in behavior. To get the system to assign them the new MIME types, you'll need to do one of two things:
1. re-upload the .jad/.cod files in question
2. (if you have enough files for that to be a pain) send us a support request and we'll tickle the system to make the change.
Sorry for the wait!