The current car has been around since 2011, so it's no surprise that BMW is working on a replacement. Although these photos are new, prototype M5s have been running around for a while now. We even have video of a car testing at the Nürburgring. The car is probably close to production ready at this point.
All of the M Division trademarks are there. Four exhaust tips, flared fenders, beefy brakes with fixed calipers, lots of tire, etc. A few things differ from the previous spy shots we've seen. The front bumper looks to be slightly reworked, with larger air intakes than before. The design of the headlights appears to be slightly different and more in line with the new 7 Series. Other than that, there's not much here that we haven't already seen.
We expect the new M5 to be powered by a twin-turbocharged V8. The Nürburgring tester sounds like it has a V8, and the M Division previously said it's not giving up on eight cylinders yet.
There are also rumors floating around that the next generation of M cars will send power to all four wheels. Audi has put Quattro in its cars for years, while Mercedes-AMG is moving most of its models to all-wheel drive. Although BMW has said that it's sticking with rear-wheel power, don't discount optional AWD for next-gen M cars.