I'm a Linux guy - but have to say .net core has impressed me.

Going back to the question - certainly in the UK it is massively popular. The company i'm at now is mainly .net, but moving to .net core, probably a majority of jobs in my area are using some flavour.

To some extent I think old school .net is holding it back. Core however will get a lot of traction, nobody wants to pay the Windows tax when they don't need to.