I've decrypted the exported key backup files before. The format was just a plain text format---pretty easy to modify if you wanted to do so. I don't know if that's the protobuf thing you're talking about or not.
The decryption part isn't too hard because you can use the fairly standard openssl command-line tool, however starting with version 3.47 the decrypted format changed from a text file containing WIF-style privkeys to a Google Protocol Buffer format. There are some advantages to the new format, and there's plenty of documentation on Google protobuf, however until someone writes some software to handle the new format, it's not particularly easy to deal with.