One of the companies I consult with makes a unit for monitoring oil condition. We recommend it for diesel trucks and other large vehicles, boats, etc. I recently had a discussion with a man who ran the service department for a large MB dealership in Newport Beach, CA for 20 years. He said the reason that MB added the oil condition sensor was because customers don't believe how far they can really go between changes - 15K in the newer models using synthetics. One thing they also found was that while the oil can last longer, the filters cannot so be sure to watch them separately.

Oil condition is a function of many things, not the least of which is its starting composition. Different additives can make the oil last longer but not forever. How you drive, where you drive, quality of fuel, filtration, weather, and so many things make it hard to really extrapolate from one engine to another. The other issue about oil change interval is how much damage are you willing to tolerate? Some people like to drive until the oil gets viscous. This is a bad thing and you should have changed long before.

As I said before, our units are a continuous monitor and it is very interesting to see the different intervals that "professional" drivers use. So, I am not sure you can ever get one single absolute answer beyond, find what works for you.

BTW- Oil testing services are a very good way to learn a lot about what is happening with your engine beyond just knowing when to change the oil.