According to Comcast, the Pace would have stopped working when 3.0 comes in, but the Motorola will keep trucking.
Considering the ATSC 3.0 specification has not been finished (and won't be until at least the end of the year), how can Comcast know if a current cable box will be compatible?
The person he spoke with has no idea what they are talking about. Cable companies don't even use ATSC on the system, and no cable set top box is able to receive the 8-VSB RF signal used by ATSC. Yes, there was a 16-VSB signal proposed for cable systems, but AFAIK no manufacturer ever produced a box and no cable company implemented it. Cable systems use Quadrature Amplitude Modulation (QAM) for digital cable and high speed data. They do use MPEG2 transport (same as OTA, older satellite and European DVB), but that is at the data or baseband level, not at RF. If/when anything changes with OTA signals, the cable company will replace their receiver/decoder with a new model, which will output MPEG 2 or 4. Most set tops manufactured in the last 5 years or so can decode both, and cable companies have devices that can transcode one to the other anyway.
What might be going on is that the system may be eliminating their analog SD channels. Even after the broadcast transition to digital, many cable systems converted the SD signal to analog in order to allow customers to continue to get service. Most Comcast systems have gone through this elimination of analog service already, but there may be a few that are still carrying analog basic channels. The main driver is to open up more bandwidth for Internet service.