> To add minimal complexity we could use as an example
> the recent design of context-menu-functions that is a hook.
>
> Then we could create a new customizable hook that can contain
> a list of functions that return the command candidates depending
> on the argument with file names.
>
> Then its possible options for such hook could include:
>
> - xdg-open-function
> - mailcap-function that adds mailcap candidates
> - dired-x-guess that adds existing dired-guess-shell-alist-default
> - Windows-specific candidates from w32-shell-execute
> - etc.

Here is the implementation: