I don't understand why people have the misconception that they pay for shopping channels on cable. Shopping channels, along with most religious channels, actually pay the TV provider a fee for carriage, lowering your overall cable bill.
I still think that TRUE Ala Cart won't work with the existing business model, and I don't think it would ever work for any land based delivery such as cable, simply because the cost to keep the network going would outpace revenue gained, and drive up the per channel costs to make up for it.
What I instead think will work is the following. You pay a flat fee for cable connection into your home, say $10 per month. This covers the local access channels, and any free-to-air channels. This would NOT cover any free channels that charge cable companies for carriage, those would cost extra. This is similar to the basic charge that we all pay for gas, electric, water, etc. to pay for the infrastructure and upkeep of the infrastructure. Any cable channel that wants to be carried "free" would be included in this basic access. Then, each channel you want to watch you would need to contact the programming service for. So, if you wanted to watch MTV, you would call Viacom and negotiate pricing for that channel. All billing would be handled by the local cable company, and in exchange for the access to the customer base and taking care of the billing, the cable company would keep a portion of the cost of that channel, say 20%.
Of course, for those that are single, they would see their cable bills go down, at least at first. But, for those with families, or who watch many TV networks, their bills would go up. But, this would eliminate the middle man (pay TV provider) and force the content providers to ask their viewers directly for money. By doing this, you are asking consumers directly what a channel is worth to THEM, and if you constantly raise the price of these channels, you'll see people start to leave for other channels. Of course, this also eliminates the ability to launch new channels (unless the programming provider offers free previews) and would likely kill many of the smaller networks, as they no longer have carriage. It would also place the burden on the programming providers to get the word out about new shows, to try to get people to subscribe to the channels. But, all of a sudden, when AMC or Viacom asks for more money, now they are asking me DIRECTLY if their channels are worth "pennies more per day", and I can make the choice rather than being forced into the decision so I can keep watching the channels I really do enjoy.