If you have a Prius you know that it comes with a button on the key fob that can turn on the air conditioner from across a parking lot, so that the interior of the car will be cool by the time you climb into the driver's seat. The reason that most cars don't have such a button is that they can't. You have to start the engine before the air compressor will work. It may seem like a small thing, but it's the beltless engine and the electric motors that control accessories that make it possible. You also get to keep your power steering and air conditioning if the engine fails, which is yet another benefit of beltless engines.
With a list of benefits like that, it's hard to believe that beltless engines won't catch on fairly quickly. After all, automobile designers are always looking for ways to make cars more fuel efficient and reliable. Who knows? In five years maybe all automobile engines will be beltless.