Maybe it already exists. I have AT&T U-verse, and it doesn't. When I'm watching TV, an advertisement comes on for another show that looks interesting - something I'd like to see. It could be expanded to cover a lot of different things - a movie promo, a concert, an event, a company, anything like that - but I want to limit this idea to additional TV programming because I think it would be really easy to implement.
When an ad comes on to promote another TV show that is coming up, I'd like to be able to press a menu button on my remote and pause the current programming. Open up the DVR programming and schedule and let me see when the show is on, add it to my DVR queue, or receive an alert when it is on.
You could expand this idea, too. If an ad comes on for a movie, let me press the same menu button and see current showtimes. A product? Go to the website or Amazon.com to order. Concert or event? Ticketmaster.com. This isn't a big stretch - nearly all of the cable providers are also internet providers. The TV box can have an internet browser built in that enables this.