Good question...I've seen some very round-looking things come out of modern CNC milling machines without ever actually turning them on a lathe, but I can't imagine it would be accurate enough to meet desired bearing tolerances (especially at 16,000 rpm). If they do throw it on a lathe with an crank-length offset bracket as you suggest, they could dial down the cutting speed a ways to limit vibration, or mount some other offset weights on the crank temporarily to balance it. Of course, it's been over a decade since I've done any machining, so who knows what's possible now.