Your PS brings us to the most reasonable solution. Have some default menu items. Provide a way to change that in settings. So, if I want to have suspend/hibernate (hybrid or not)/power off, I can do that too. And it is not complicated - Gnome devs simply refuse to do it.
Sensible defaults are great. Inability to customise trivial things is not. And no, writing code (i.e. extensions) for every possible combo is not the way to do it.