Well, we have packer, filesystem and lister plugis. Then, why not command line plugin?
What I have in mind?
I type some string in command line, if TC doesn't reconize it then shows a window and ignore it. A command plugin could catch this string (command) and react to it. Inspired from Dave's Searchbar.
Examples:

If I type "4+2" then a command plugin returns 6
to the command line.

If I type "x=3", the plugin return a nul string, later I type x+2, then plugin returns 5 to the command line.

If I type "alarm 14:00", the plugin remaind in background until and at 14:00 shows a message box.

It could execute internet searches. "gg something" opens a internet browser with the google's search of "something"

Or, for instance, a command plugin could execute totalcommander 'scripts'. Like batch files..
Several command line plugins can be ordered for priorty, like lister plugins.
Wath do you think about?
I hope you understand, sorry for bad english.