Many people don't seem to understand the internals of all this... MonoDevelop is the core of XamarinStudio and Visual Studio for MAC, so essentially when these guys add features they are in reality adding them to monodevelop. So think of it as:
Visual Studio Mac = MonoDevelop + macOS extensions
Xamarin Studio = MonoDevelop + extensions
MonoDevelop = Libraries, ASP.Net, GTK#, Xwt, Console Apps, etc.
What's important here is that porting over the real VS to Mac or even Linux is not practical. You won't also see mfc/win32 support on mac or linux (on the foreseeable future) because those are extremely tied to the windows architecture which is far from being compatible with unix, most people just don't get it. Same case for developing say, iOS applications, you just can't do that without macOS because you need the tooling, so its not really up to Microsoft.
What I think could be accomplished relatively easy is a XamarinStudio/VisualStudio/Monodevelop on Linux with support for Android development since you already have the tooling available there, the IDE would just wrap up the core code/tools. Also, there is no truly multiplatform desktop framework as each platform has its intricacies but there's an actual toolkit (poorly named, btw) called Xwt which is what monodevelop uses in some parts and draws native widgets depending on the platform is running, something like what Qt does.
Visual Studio Mac = MonoDevelop + macOS extensions
Xamarin Studio = MonoDevelop + extensions
MonoDevelop = Libraries, ASP.Net, GTK#, Xwt, Console Apps, etc.
What's important here is that porting over the real VS to Mac or even Linux is not practical. You won't also see mfc/win32 support on mac or linux (on the foreseeable future) because those are extremely tied to the windows architecture which is far from being compatible with unix, most people just don't get it. Same case for developing say, iOS applications, you just can't do that without macOS because you need the tooling, so its not really up to Microsoft.
What I think could be accomplished relatively easy is a XamarinStudio/VisualStudio/Monodevelop on Linux with support for Android development since you already have the tooling available there, the IDE would just wrap up the core code/tools. Also, there is no truly multiplatform desktop framework as each platform has its intricacies but there's an actual toolkit (poorly named, btw) called Xwt which is what monodevelop uses in some parts and draws native widgets depending on the platform is running, something like what Qt does.