I think I have finally been able to get the closest thing to adding new actions to #shortcuts with #scriptable as I can get.
Here is a demo of creating some "tools" that you can run in scriptable or shortcuts. The UI that you see in scriptable also allows you to create the shortcuts actions to invoke it (another shortcuts is needed to actually convert to the right format). These will be put in your clipboard and you can paste them to the shortcuts you want to add them to with minimal changes required. You can even see in the demo that the parameters are validated.






