Unlikely, doing that would mean pretty much redeveloping large parts of Win32, since it is fundamental Win32 decisions that lead to the limitations involved. And that in itself would be not only an enormous job, but a compatibility nightmare. And even after
all that it might not even be fixable without breaking basic Win32 assumptions - remember it's not necessarily just layering, but the ability to truly treat it as a WPF control, including applying transformations, animations or embedding the control onto a
3D surface whilst remaining functional.
Given that Trident no longer has any actual dependencies on real Win32 controls, it would probably be easier to port that into WPF via C++/CLI if they wanted to fix that. It's questionable whether that would have any benefit for Microsoft though, given it's
not something they necessarily need themselves. I still think it would be a useful third party control though.
I hear WebKit has a reasonably portable back end. I wonder if it could be ported to render to a Direct3D surface which could then better interop with WPF via D3DImage.