Having worked for a large Canadian cable company for the last two years, I can tell you with 100% certainty that this will NEVER happen until everything is digital. The way land-based analog cable (First 60 or so channels - everything you can get without a box) currently works is through a filtering system that works like this:
You order all the channels : no filters
You order a bundel with packs 1 and 2 and basic: the reminaing channels (pack 3) are filtered off.
You only want basic: You get all four filters.
These filters are done AT YOUR HOME (Inside the Grey CSE's on the side of your houses, in a PED, or on a drop line from an antenna. Each of these filters costs about 5 bucks a piece. So that means at 60 channels, if you only choose to watch CBC, Space and MTV, they have put 57 filters costing about $285 (Cdn. Dollars).
Not only is it a cost issue, but these things are pretty inaccurate and can only get a range of channels properly. So if you were selling channel by channel, odds are if you bought one channel, they would have to give you 2 or 3 channels free in order to be able to receive that one channel.
Another problem is actually installing the things, working with four color coded filters is a breeze. Working with 60 different filters is going to create some problems.
Anyways, there's some insite into the cable industry for ya. Until they get a digital box in every home, this will not happen.