What's a "rockstar project"? :-)

One that gets high, trashes the room, drives an expensive car into the hotel swimming pool, and breaks up the band to release a mediocre solo project, then has to go back to touring with the band when the money runs out.

.NET is an enterprise framework, mostly used in B2B software, which is rarely "rockstar"

Anyway, who cares about it, when the bulk of job vacancies are offered by the enterprise. It's a lot easier to find a junior dev role for a .NET dev than for a Ruby dev for example: https://www.youtube.com/watch?v=ZUgNy-okDQ4

It will be. Just a matter of time. As things stabilize; Unity Engine will certainly use it moving on. They could already be using it. Not certain; It just doesn't make sense starting a new project with old .NET Framework from now on;

Until everyone has put their golden eggs on .NET Core basket, it makes plenty of sense.

Absolutely. It depends on the project and situation. But it'll start making less and less sense. Personally I've moved on at .NET Core 2. Never looked back; But my area is game development. Most people on .NET are doing Web Development; There it could still make sense to stay at old and proved .NET Framework;

dot.net and bing.com are running under aspnet core 3.0

Um dogfooding doesn't count.

Tencent - pretty rockstar in China.

You don't use StackOverflow, ever?

That's pretty much it.