That's already widely done in the US.

If you plug in an antenna and scan for local channels, what used to be one analog TV channel on colloquially-named "channel 7" in the defined channel 7 frequency range will now be seen as "channel 7-1" which is often (but not always!) actually broadcast on the old frequency. During the ATSC transition, it was important to retain the branding and consumer memory of "channel 7" even when the RF transport frequency changed.

The transition opened the ability to have an arbitrary number of digital subchannels, 7-2, 7-3, etc etc. The total bitrate available on a given ATSC broadcast is fixed, but it can be partitioned among multiple MPEG streams. The typical setup is one (occasional two) HD channels and several SD channels. Obviously there's a balancing act between bitrate and visual quality for each subchannel. It's often used as a way to broadcast older (read: cheaper) syndicated SD content on which they can run more ads while keeping the main HD channel quality reasonably acceptable.