Just because the Pistons acquired Brandon Jennings in a sign-and-trade deal with the Bucks doesn't mean they've lost interest in Rajon Rondo. In fact, they could eventually use Jennings as a trade chip and seek to acquire Rondo. There are going to be several interested parties in Rondo, and that number could increase when he shows he's fully recovered from anterior cruciate ligament surgery.
The Pistons got Jennings on a little bit of a steal ($8 million per year for a starting-caliber point guard coming off his rookie contract is pretty good), so the contract is movable. If he shows a good first half of the season, Boston might be intrigued. The trick with Boston is that they're not looking to build around a player like Jennings, they're looking to eventually move him when the next superstar or superstars come available, the same way they put together the 2008 Big 3.
So Jennings could look much better at the trade deadline then he does now. Similarly, Rondo could look like more of a bargain if he struggles out of the gate upon his return from ACL surgery, or if he looks fine but the Celtics are an outright disaster.
It's an interesting idea, and Rondo might be a better fit for the Pistons as a pure creator. Much of it will hinge on what Jennings does, coming off a free agency period where he has to feel disrespected.