Wasn't that long ago that the Honda CBX 1000 (an 1100cc IL6) made it's 3 year run. Overly complicated and hard to tune, nobody thought that an in-line six belonged on a bike. Go figure they're becoming serious collector items now. According to Leno the valve adjustment requires dropping the engine.
...I'm willing to be the CBX was inspired by some of Honda's race bikes, such as the successful mid sixties Honda RC166 sporting a 250cc IL6 with between 60 and 70 horsepower, a 20k redline, a 7 speed transmission, and an absolutely glorious exhaust note. Keep the revs up, there's no flywheel!
With fuel injection and hydraulic valves, more cylinders are easier to pull off for an every day rider. BMW is selling a six cylinder now, and the flathead V8 in this one-off build doesn't have a whole lot more displacement than the American big twins. I'd be willing to bet we'll see an 8 cylinder production bike in the next 30 years, though I won't place a wager on the cylinder configuration.
