What's the current state of this? Being able to develop with C# in the browser would be a dream, but the last I checked it wasn't really ready for any kind of serious use.
It still carries huge "don't use for production" warnings, and only parts of it are slated for stabilizing in Dotnet Core 3.0. That said, it's fairly usable today, and I think there's enough interest in it that I'd be really surprised to see them abandon it at this point. I think it's worth considering for a personal project or something internal where you are going to do the back end in C# anyway.
It's still in alpha stage but Blazor is one of the most exciting new developments and has seen tremendous feedback from the community so it's developing rapidly.
The component model (Razor Components) for the UI is already committed to ship in .NET 3.0 so it can be used in server-side views, but the client-side WASM framework doesn't have a release date yet.