I don't feel the adv field is becoming in any way homgenized, with inline triples, vertical twins, L twins and the as always unique, boxer layout. BMW learned and admitted, that with development of the HP2S dohc air / oil cooled format, it had reached the peak outputs this motor could yield, without sacrificing reliability.
The sad fact in this evolution is that BMW, with their finger in seemingly every damn piehole segment of motorcycling, won't have the flexability to maintain production of two distinct boxer formats, for any given length of time. I don't see the air / oil cooled motor staying in production long, once the w/c boxer is up and running and yes from a purist standpoint, that is a shame. But this same cycle has been repeating, since the dawn of motorcycling and usually the biggest antagonists of change, are the one's most impressed with the demo rides.
I still have BIG ISSUES, with the Castiglione bros pulling the plug on the Mille bevel, immediately after assuming ownership of Ducati, but that ship sailed a long time ago...