ESRI plans to support the WMTS ( Web Map Tiling Service - OGC specification). The support for this will be Post 10.0 final. The wms-c effort is an OSGEO effort, and ESRI will instead go with the OGC sponsored WMTS specification. The specification has been voted on at OGC and will be declared an "implementation spec" soon.
Thanks.
Satish Sankaran
ESRI