I know this has probably been discussed or mentioned, but i can't find where
There are 2 reasons I think an extension is important.
1. (LESS important) People like them. They help people identify a program and it feels natural to find applications by filetype.
2. (MORE important) An extension would allow specific treatment for application files. File managers could have specific functions and reactions to these files, like pulling icons or easy launching. Users could set specific permissions for all files of that type. Metadata tracking/indexing systems like nepomuk and zeitgeist could separate these files as a different class.
I think this change is necessary and should be worked on as soon as possible. i can't really see it as a hard goal since i believe this is loosely a successor of the klik 2 project, which used ".cmg"
examples: .lxp (linux executable package) .amg (appimage), .cmg (compressed image?) etc....