I headed to Dell’s web site and ran a site-wide search for “M6700″ or “M4700″ and got some signs that the machines are coming. How soon, nobody knows yet.
Also no signs of the specs yet, but I’ll keep you posted if I find anything.
In the mean time here’s what I found:
Dell Intel Chipset Software Installation Utility drivers supporting the upcoming M6700:
Dell Client Configuration Toolkit (CCTK) listing supported systems M4700 and M6700:

