Yes - Wiring++ is still very much going to happen. But, as always, we have extremely limited resources, and very few volunteers to work on the software.
An objective of the next version of Wiring is to have the Framework become extremely easy to port to new platforms. Robert Wessels (Texas Instruments' Energia project), Rei Vilo (embedXcode) , Marti Bolivar (LeafLabs), and Hernando Barragan have put an enormous effort into changing the "Build Unit" into something that will make porting to new processors and boards extremely easy.
The D20 and other ARM processors should be relatively easy to add once we release the next version of the IDE as long as they have a port of the GNU C++ compiler (and tools).
As for new additions to Wiring, Ed Baafi (from Modkit) had suggested adding a threading and event model to the Framework (which you may have seen at the San Mateo Maker Faire). It was a brilliant idea, but possibly a bit too advanced for general users to use. So, we've begun a new approach to the threading idea and, hopefully, we'll be able to show it off soon.
Since this is an open source project with no funding (no, not even from Arduino), the development happens when it happens. We don't have deadlines, and we are restricted by the resources we have, which consists of, at the time of writing, just the three of us (Alex, Hernando and me).
If you have the passion, time, and knowledge to work on the Wiring Project, we'd, more than anything, love to have you help us with the project. Funding the project through donations would also help.