[judah]

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.