Hi Michael. I wasn't claiming at all that the Rhino UI isn't flawed. Quite the opposite, I'm looking forward to seeing what they are developing! Most of the time I work with a maximum of one or two custom floating toolbars and nothing more. It boggles my mind when other users post screenshots littered with hundreds of buttons everywhere. My attention span is so short, I feel completely lost... :)

About the pre-selection, V4 actually does have pre-selection of faces and edges if you press SHIFT+CTRL+LMB. Some of the commands even work using the input. Such as pre-selecting a face and then running ExtrudeSrf. But it won't filter the command for you as MoI is able to do. You have to enter the specific command on your own, so there is little benefit for modeling tools. But it does work for analytic commands such as selecting an edge and running _Length or _SplitEdge. This is an undocumented feature which I imagine will lead to improved command filtering down the road. Tsplines can do pre-selection rollovers so I imagine this component was added by McNeel to support them. Possibly the mechanism is one and the same?

And yes, you are right about the existing "ecosystem" of plugins. They make it difficult to make big changes and already there is a lockdown of the SDK until V6. That's both a good and bad thing for its users, as V4-complied plugins will run in V5 but some changes to current features may be delayed...

jonah