While you make some good points, I would suggest that cloud computing can far exceed the performance of desktop computers. Deep learning and other cloud based AI algorithms/platforms are performing remarkably well these days, and I would ask you to try Onshape as it is a full fledged engineering CAD system in the cloud brought to you by the inventors of the #1 CAD system, Solidworks. So, it’s definitely possible. I would say the current SU web version is quite simple compared to it, and not a good example of what the future portends.
As far as plugins go, I would think they might create a smart translator which can mostly convert the Ruby to the necessary new plugin language. At least that’s how I would approach the problem. And, it doesn’t require too much in the way of current developer input, as most all SU plugins have visible code, so such a translator can be put into an automated test environment.
Furthermore, most all high end CAD/3D packages (Autodesk and comparable) all have cloud components to them. And some, including Autodesk, cannot operate without an Internet connection.
So, yes there are some hurdles, and perhaps Trimble doesn’t have the requisite skilled programmers. The devil is always in the details.
Lastly, consider this scenario. Say a future version of SU PRO ran on a TRIMBLE cloud based virtual workstation, and used the native plugins just as they are. You could subscribe and run it from any Chrome browser on any device. The plugins are always updated. You can work from anywhere on any good or lame computer. As I mentioned before, I have already used such a system on my Chromebook. I have an external monitor and two screens and I can use SketchUp just as if I were at home on my big rig.
Now, how to wrap all of this into a nice package someone would be willing to pay for? I have ideas.