Honestly, I think the entire cli module should be deprecated and reworked. It was quickly put together to make the examples work, and it doesn't have much of a design. Extending it is something I'd like to avoid until it is reworked.

Yes, it's a bit tedious to use.
It would be really cool, if one could just hand it the class name of the Elaboratable,
it would scan it via reflection and instantiate it on its own by default, so that no
extra code would be needed to do the basic tasks like generate/simulate/show.
Anyway, thanks for taking the time.

I think I found a more elegant solution.
A commandline tool which already can handle show, and also will handle generation and other common tasks.
https://github.com/hansfbaier/nmigen-tool