Right now we're finishing up new versions of our existing WPF products, adding another WPF product (already ready to go), and are going to be starting a WPF bundle of all our WPF controls. All this is going to be released at the same time in the coming weeks. After that, we will probably begin on some serious implementation of SyntaxEditor for WPF.
One thing we'd like to look into doing is building a common document/parsing assembly that could be shared between the WinForms and WPF versions of SyntaxEditor. This would be part of SyntaxEditor for WPF and possibly a porting of a SyntaxEditor 5.0. Then there would be separate assembly used for providing the UI. The nice thing about that would be that it would make it easier for us to maintain and also for WinForms customers to switch to WPF down the road if they choose.
However when we do make the SyntaxEditor for WPF, one thing to note is that while it will be usable in XBAPs, it probably won't be Silverlight compatible since Silverlight doesn't support much of the core WPF framework.
If you'd like to discuss SyntaxEditor for WPF in more detail, feel free to email us.