Given the vast success of Wikipedia, it still seems odd to me that the 'old' Encyclopedia companies, who understandably had their hats handed to them from 2000-2015 ... haven't really seemed able to even take a real shot at being an alternative. Even the UI to these things still feel clumsy and outdated, made by 'book' people.

The UK gov. uses BBC as a Foreign Policy tool of sorts, I'm surprised they haven't done a similar with with their encyclopedia companies. Socializing them and having some kind of quasi-public editing by 'sanctioned' individuals (i.e. professionals in a field) may yield something usable on the relatively cheap.

Wikipedia is explicitly designed to be legally mirrorable and forkable and several mirrors and forks of it exist.

On the universal scale on which Wikipedia operates I don't see any, however in particular knowledge domains others seem much better.

Eg Stanford encyclopedia of philosophy.

This is presumably because Wikipedia's brilliant democratic approach has its inevitable downsides which professionally curated resources don't have to deal with.

As far as a universalist resource goes, Quora showed promise in it's early days, and StackExchange still has a powerful presence but I'm not aware of anything that directly competes at the same level of similar knowledge value.