I'm not sure I have any more insight than anyone else. What I can say is that even with 200+bhp, torque that dwarfs a K1300S in any gear and at any revs, on a bike weighing almost the same as the K1300S, after 15,000 miles, I've still not had to adjust the chain. That doesn't mean it's not been adjusted, only that adjustment requirements have, so far, managed to align with servicing and tyre replacement.
I expect that the BMW chain will stretch and will need replacing but rather than it taking 5000 to 20000 miles as with a "normal" chain, depending on how it's looked after, it'll be 40,000 to 60,000 miles and adjustment intervals for stretch will align with service intervals so will be done by your friendly BMW dealer.