I've travelled with soft panniers, though not the latest generation and only within Europe. But from your very thoughtful post I definitely agree with the desire for light weight (in bike and luggage), though I have a few reservations about the really light weight trail bikes (including the 690/701) being great mile munchers, particularly if you're venturing far from civilisation and rescue services. As you quite rightly say, you can do it on anything, but still some bikes are better than others.

Your reasoning is also why I'm 99% sure my next bike is going to be a 790 Adventure, and I've been thinking about the best luggage to use on this. My current thinking is a rack with hard top box, because as you say hard luggage is less attractive to the casual thief. A place for laptop, camera. etc. On the sides, supported by racks, soft bags which I plan to secure with Pacsafe cables to prevent casual opening and removal. Sleeping bag, tent and maybe spare waterproofs in a dry bag in a Pacsafe net bungeed on the back seat.

Maybe that's a bit of a faff but I'm a tad paranoid about theft on the road. I know a determined thief will get in anyway but I reckon 99% is opportunist and that can be deterred.

As for seating, I'm looking at lightweight camp chairs, and as for leg protection in a spill, that steers me towards soft panniers. HTH