GPS will not be certified for 'sole means.'

Period.

It depends on what "sole means" means. GPS and its augmentations will
probably never be the only navigation system provided. However, it appears
that the FAA will permit non-commercial operators to fly IFR with only WAAS
and GPS - see the current NOTAM:

http://www1.faa.gov/NTAP/NTAP03JUL10/GEN03003.HTM

Note in particular the last paragraph:

"Unlike TSO-C129 avionics, which were certified as a supplement to other
means of navigation, WAAS avionics are evaluated without reliance on other
navigation systems. As such, installation of WAAS avionics does not require
the aircraft to have other equipment appropriate to the route to be flown."

Barry