As dug up by Bimmerpost, the patent drawing above (and more at the link below) shows what appears to be a twin-turbocharged V-6 engine. Worst of all for fans of the straight six is that it's rumored to be going under the hood of the next M3.
That's right: not only have we lost all of our naturally aspirated M cars (not a huge loss to some) but the straight six may be gone from all but the limited-edition 1-Series M Coupe soon.
Excitingly, however, the schematic appears to describe not a parallel twin-turbo setup as you'd commonly expect with one turbo per bank, but a sequential turbo layout, with all six cylinders routed through a single turbo, then optionally to exhaust or through the second. This layout could maximize power throughout the rev range while further enhancing its ability to deliver solid fuel economy in normal driving.
It could also explain, possibly, the rumored three-turbo layout for the next M3: one turbo per bank, plus a sequential third that optionally engages for more top-end power. That, however, is little more than wild speculation.
Whatever BMW has up its corporate sleeve, however, M3 fans are sure to be up in arms over the idea of a V-6.