Currently, the CIX is using an SMDS cloud from PAC*BELL. SMDS works pretty well. Unfortunately, the Cisco software does not permit these to be SSE-switched. Hosts attached via the CIX appear to get ethernet-like speed (when attached to the SMDS via T3).
The T1 service will be retired at the end of this year. The folks on this service will probably move to SMDS or make use of another mechanism.
The SMDS service is completely open. Paul expects that SSE switching will become possible with SMDS. The CIX may operate some route servers to make it easier to aggregate BGP sessions.