According to this blog post by Soma, WinFX is now going to be named .NET 3.0.
Now on one hand this makes sense. There's no doubt that WinFX introduces major functionality to .NET. Windows Presentation Foundation is the effective successor to Windows Forms after all - how much more major can you get??
On the other hand, the new .NET 3.0 doesn't break any .NET 2.0 code, and yet it "includes" .NET 2.0. All .NET 3.0 does is add new stuff. Typically, when I think of a major version number changing, I expect that I'll have to retest everything and that much of my stuff might break or be affected. None of that is happening here.
Even changing from .NET 1.0 to 1.1 brought tons of headaches (if you used Remoting or Enterprise Services at least). And that was a point release. Yet here we have a major version change that doesn't change any existing bits.
I guess it just goes to show that there are no hard-and-fast rules in the software industry ;)
In any case, there's no doubt that Microsoft will reduce confusion overall by keeping everything under the .NET moniker, so I think this is a wise move.