Rhino really isn't the alternative I'm looking at. It has a relatively bad GUI (as most CAD tools seem to enjoy).
But I'm working with many 3D applications and there are IMO several well working solutions to this kind of problem.

Having a dropdown menu with all installed plugins wouldn't directly lead to GUI-mageddon. ;-)

It could be very simple with sub-menus created from file system subfolders, so you could have folders for Points/Curves/Solids/etc. put the respective scripts in there and have them show up in equally named submenus.
Just an example though.

I personally enjoy MoI 10 times more now with Max' script installed :-)

And I have totally zero problem if it will change somehow in 3 years...

Cheers,

Tom