Getting back to pillion comfort.
I would imagine that most GS pillions are going to be female, and some may be larger than a size 12 ?
I believe that it's the grab rail and the positioning of the panniers which may make this bike uncomfortable for some pillions on long journeys.
Anyone over a size 12 and especially attired in heavy winter riding gear is going to find that the grab rail gives very little room to shuffle and in fact will start to dig in after a while,it's also a little to high to be in a natural grab position.
The vario panniers also appear to mount slightly to far forward therefore impeding the pillions ability to shift themselves on the balls of their feet.
So for anyone who regularly carries a pillion over any distance and is considering a new lc/wc/wb think long and hard about your luggage.