It's probably the closest contender [1], but its non-Windows story is still a handicap, as is Microsoft's habit of making sweeping incompatible changes to their development platforms every 5-6 years.
[1]: A different philosophy that gives more control to the user in exchange for explicitness puts it ahead in some areas (structs) and behind in others (compilation quality, GC), but as a runtime engineer it's "technologically" behind (I work on OpenJDK so I'm biased, but I came to work on OpenJDK because that's where most interesting innovation in runtimes happens).
Disappointed? Not at all! I worked with it many years ago.
Whilst WCF made some notable improvements over what existed within the ecosystem before it, it was still a sprawling, complex PITA and full of developer friction. Killing it off in this case was definitely the right thing to do :-)
Do you have anything to support that expression trees are being sunset? I haven't seen anything of the sort, unless you are talking about a deprecated library that has been replaced. But System.Linq.Expressions is still around.
.NET Core's cross-platform tools and ecosystem is wonderful. I'm working on a small team and the devs are using Windows, Mac, and Linux. CI builds are a mix of Windows and Linux, deploying to Linux.
I think their biggest weakness now is branding (.NET vs .NET Core). This will be fixed with .NET 5, which merges the two and will make all flavors of .NET cross-platform.
[1]: A different philosophy that gives more control to the user in exchange for explicitness puts it ahead in some areas (structs) and behind in others (compilation quality, GC), but as a runtime engineer it's "technologically" behind (I work on OpenJDK so I'm biased, but I came to work on OpenJDK because that's where most interesting innovation in runtimes happens).