I always felt that CableCARD was an over-engineed solution to what feels like a simple problem - essentially it ships a cablebox inside a card that can be inserted into another cablebox type thing - all to support the massive DRM based empire cable companies have built.
To me it seems like there are simpler and more cost effective solutions, and from what I've heard from people who've used CableCARDs - probably more reliable solutions.
I'm not surprised that they didn't catch on, but I am a little disapointed, because for all their faults, there was at least an attempt to make digital cable services interoperable.