That seems really problematic though. I could be on a text editor, or the terminal or anywhere else requiring text input and might not be expecting this behaviour.

Sorry, I edited my comment not to say spacebar, since space clearly wouldn't work.

On the other hand, you might be able to do it with some key or combination that is less commonly used?

I don't get why Apple doesn't provide an API for registering global key bindings. All it needs is user permission for a binding to be registered, and some kind of preference pane that shows you an overview of registered bindings.

They do.