I have the same problem - both my front tires are each worn both on the inner and outer part of the tire. The middle part of the tire looks good, but the outer parts are worn (could be from cornering? although i haven't driven the car hard at all).
Noticed the same problem looking at other cars. Don't know what could cause this, tire pressure was always good (specified values on the driver door). Running on OE Continental SSR.
Rear tires look good, so only the fronts have this issue.
BMW 320 dA LCI, BMW PPK - 197HP, 2010, sapphire black, steptronic