Hi Kentico Dev,
The reason for lack of guidance on such a thing I believe it would have been much easier sharing/publishing widgets as a code, not via nugget packages. Have you looked at examples of widgets here in the marketplace? I think this will be the easiest way of sharing things like widgets, sections, templates, etc.
Nuget packages are more suitable for distributing more complicated logic like Dynamic Routing.
The only kind of nugget package generation approach I've seen was Sharable Component Boilerplate by Trevor Fayas on GitHub. Probably it will help you.