I just spoke with Bruno de Prato in Italy, who has seen the front suspension mechanism that BMW is using on its new Boxer prototype. It's not the Hossack design, which uses twin A-arms; it's the design devised by another Englishman in the early 1970s, whose name currently escapes me. We'll just call it the BMW design for now, though Erik Buell also holds patents on a related, but not identical, front suspension.
The new Boxer uses two telescopic legs, much like a conventional motorcycle front suspension. But in place of a lower triple clamp, the BMW design uses a fork brace just above the front tire. A ball joint connects the brace to the point of an A-arm, and that A-arm, roughly parallel to the ground, pivots (vertically only) on the frame. At the top, the telescopic legs are joined by what appears to be a conventional triple clamp; however, it pivots in two planes, either on a ball joint or --probably for lower steering friction -- on compound, roller-bearing supported axles. So the forks steer not on a standard steering head, but pivot about a line drawn between these top and bottom ball joints.
Why go to all this trouble to still have sliding joints in the telescopic legs transmitting braking loads? Well, those loads are much reduced by decreasing their leverage. Instead of reacting them at lower triple-clamp level, they're now reacted just above the front tire -- giving perhaps a 25 percent reduction in bending forces on the fork legs. This should reduce friction compared to a conventional front suspension, and allow lighter, smaller-diameter fork legs to achieve the same stiffness.
Second, less pro-dive effect can be built into the front suspension than on an conventional motorcycle. The geometry of the A-arm movement with wheel movement can be jiggered to make a motorcycle dive less under braking.
Last, compared to almost any other front suspension alternative to the conventional telescopic fork, this design maintains one of teleforks great virtues: The direct link between handlebar and front wheel. It uses no complicated linkage with stiffness, bearing, and bump-steer issues to be dealt with.
Will BMW still use this system on the production bike? No final word on that yet, but I would bet that they do.