Hmm on reflection, while I was originally gonna go all Unity for editors and tools (for the easy cross-platform goodness)... having had a look at how involved recreating a UI like that is, I'm now thinking these will be Windows apps, built in C# and .NET, and they will have the ability to embed a Unity process renderer (such as a 3d machine renderer in the Layout Editor) within that interface.
So rather than the previous video, the interface will actually look a bit more like MFME As it'll just be Windows stuff - here's an example of something I knocked up before using that:
So the UI for the tools, they will look and handle much more like the standard Windows interface (and will only run on Windows for now).