Unless of course they push to make VS cross platform. I wouldn't be surprised if this is in the works. There has been a huge push at MS to become more cross platform with their product offerings. They must know a lot of their developers run OSX with a Windows VM just to run VS. I know pretty much our entire team does that.
As someone who has worked with Visual Studio and integration APIs for a long time, a port of VS across platforms would be a huge undertaking. A rewrite, essentially.
Visual Studio is heavily tied to WPF (Windows-only) presentation framework, COM (Windows-only) for communication across components and plugins, as well as bits of native legacy code throughout (Windows-only.)
Truly, you're looking at rewriting Visual Studio to get it on OSX. Heck, MS would probably be better off just buying Scrawl and rebranding it as Visual Studio for Mac.
And remember: while .NET is going cross-platform, there are no public plans for a cross-platform UI toolkit; there is no cross platform WinForms or WPF from Microsoft.
If Microsoft made VS cross platform, they would make a much more lightweight, modular IDE aimed at (initially) C#,VB,F# and javascript. They'd be able to leave out decades of that old COM/Win32/C++ cruft.
Essentially, this is what they would make. Or, they could simply buy this...
