It's not incredibly surprising to me (though I am surprised there was no forward announcement before the preview release). It became clear a while back that Microsoft was looking to expand it's developer environment to other platforms when they announced ports for .NET and SQL Server. Don't forget that Visual Studio Code has been cross-platform since inception.

Right, but I thought that VS Code was going to the only concession to cross-platform coding. It's cross-platform, but built on completely different tech and obviously designed for a different kind of workflow to Visual Studio. I assumed it was intended to be a "gateway drug" to lure a few more people to fully leaded Visual Studio.

There will be a mindshare battle between .Net, Java, and Go.

Definitely a shocker. Visual Studio is by far the most comprehensive IDE. How will this play out for all the features that available on Windows that may not work on a Mac? What does this mean for Java? Lots of things still need to happen but the difference is getting slimmer.

What's funny that it is rebranded Monodevelop.

Actually rebranded MonoDevelop rebranded Xamarin Studio. But with support for .net core which brings amazing power to non-windows.

I don't know, the fact that they are willing to put the Visual Studio name on it would suggest big plans.

It's not what you think. It's not about Windows or Windows Phone development on Mac, it doesn't support MSVS plugins... it's basically just Xamarin for Mac, iOS and Android development on Mac using Mono/CLR.