I think the lack of sub-channels has more to do with channel density and logistics then CRTC requirements.  Take Toronto for example, there are about 10 stations, maybe you can pick up another 10 or 15 from the US, there are 53 channel positions running from 6-59 so less then half the potention is realised, and Toronto is one of the largest markets.   You could add some new content, for example CBC could piggyback newsworld on a number of stations or offer French as a subchannel in markets where it doesn't currently exist, but are those markets large enough to justfy the cost?