I am not sure I understand the problem, but I have been using Dexpot on Win 8 (DP, CP and now RP) just fine. The window key works fine for all desktops. The only bad thing is that we don't get thumbnails for Metro applications but I think thats not even possible with the current API.
A fresh install solved the problem. I would want to find out what caused this (an old 1.6 beta install with custom keyboard shortcuts was on my old setup) but I'm too lazy so I just deleted the old one. The RC will auto-update to the final version, right?