These are great ideas to discuss. It would be important to make simple things as simple as possible to do in Slicer.
If we get to know any specific issue then we can address that. But addressing usability in general is really hard.
I’m not a believer of having a “simple mode” for powerful applications, mostly because all the attempts that I have seen have mostly failed: in applications that I did not know, they did not make learning any easier; in applications that I knew already, it just made things harder to access. But we can certainly evaluate this option for Slicer, maybe we can do better.
Predefined workspaces/perspectives optimized for certain tasks seem to be a good idea, too, but based on my experience with various software, they do not help much; and flexible layouts make the software more difficult to learn because my screen always looks completely different than those shown in examples and tutorials. Experts don’t use predefined workspaces much either, because they rather set up their highly optimized workspace; but ability to customize layout and save/restore it is a useful feature for experts.