Recently I’ve been working on the layout of tabs and panels in grasshopper 2.0 and most of the things you’ve mentioned are possible now. The second layer of tabs hasn’t been added, but right now you can select one out of various user defined layouts from the menu. Turning that into a toolbar/tab row would be trivial.
As for installation, it is my fervent hope that all plugins will be managed by Yak (i.e PackageManager), with only very special cases requiring some parallel deployment mechanism.