For a very long time I have believed BMW's boxer bikes owed their success much more to quality than to engine layout. The opposed twin is, after all, the worst of all choices for a motorcycle, and would not be employed even by BMW were it not a tradition there.
Yes, yes, yes. It is in near-perfect primary and secondary balance, its perfection spoiled only by the offset between the cylinder centerlines. BUT...
Reciprocating imbalance is not the only or even the most potent of sources of shaking. As it happens, torque reaction is the biggest shaker in big twins. Every time one of those big cylinders fire, the crank, flywheel, and all the other rotating bits get driven one way while the presumably stationary hardware (crankcase, cylinders, etc.) go the other way.
Torque-pulse shaking is fairly well subdued when the engine has its crank disposed across the longitudinal axis of the motorcycle, but takes over when crank and chassis point the same direction. This is why Ducati's 90-degree V-twin feels smoother than Moto Guzzi's 90-degree V-twin. The role of torque pulsing is revealed in the fact that BMW's "perfectly balanced" opposed twin does not feel smoother than a Moto Guzzi of the same displacement, and shakes more than the Ducati.
And, of course, the 90-degree V-twin has a stronger single-throw crankshaft, inherently simpler valve gear, and much less convoluted intake manifolding. It has the good cooling of an opposed twin, and its cylinderheads aren't as likely to become an embarrassment when cornering.
On the other hand, BMW's flat twin is made by BMW, which has demonstrated over many decades that it can build a highly successful motorcycle around a flawed engine layout. I very much doubt BMW had the least intention of creating a new boxer motor after introducing its in-line fours and triples. That it has done so tells us more about human nature than technology. The deficiencies of the flat-twin layout notwithstanding, people liked the boxer Beemer, and don't much give a damn about what BMW's engineers unquestionably know, or what I may say.
Allow me to make some predictions: The BMW faithful will heap scorn on me for the comments made here; they will buy a bunch of the new boxer bikes; and they won't be sorry they did. So much for theory.