In answer to stampeder post #9:
If this request came from a Canadian broadcaster (I think I know which one) then I'm curious as to how developed the idea may or may not be at this time within the CRTC
It appears that as of March 2010, the CRTC is condoning more services through multiplexing.
Broadcasting Notice of Consultation CRTC 2010-169
Route reference(s): 2009-411, 2009-614
Ottawa, 22 March 2010
1. Canadian television is in the process of converting its over-the-air transmitters from analog to digital. The transition to digital television (DTV) will provide significant benefits to Canadians. In addition to providing television viewers with better picture and sound, including high definition programming, and allowing for more services through multiplexing,1 it will make spectrum available for public safety uses and greater wireless competition and innovation through the repurposing of channels 52 to 69.
1 Multiplexing is the use of one digital transmitter by one or more broadcasters to transmit several programs at the same time.