If you somehow get a file with an unknown extension:
- by downloading it
- by receiving from a colleague by mail
- by finding it inside an optical medium (CD)
... and you do not know what program is normally used to open it:
the OS should pop up a dialog
- STATING that currently this file extension / filetype is not associated with any program;
- SHOWING some programs you have installed that might be used to open such file extension;
- SUGGESTING you could look for (via SoftwareManager) some not-yet-installed application that might handle the filetype.
It seems to fit well into usability and elegance principles of Mint, and it is kind of "vanilla" in other OSes, I guess.