Well, I've now test-ridden both the GTL and the GT at 2 local dealers, and can make a comparison of the two bikes, as well as to my '08 new-gen K1200GT.
1: Very relaxed seating position, which is great for low speed maneuvering, with a very low seat height.,
2: Super maneuverable, and feels 200 pounds lighter than its weight. Somehow combines cornering agility of a great naked bike with the high speed stability of a tourer. A great chassis. ESA settings worked well for me, selected changes very noticeable and useful.
3: Engine is awesome, with a great sound, absolutely no vibration through bars or pegs, and excellent power, with butt-dyno power to weight ratio about like my K1200GT. It revs freely and quickly, has just right amount of flywheel effect.
4: Fit and finish excellent
5: Dynamic cornering lights were not evaluated by me, but seem great from on-bike videos
6: I started out in Rain mode, at dealer's requirement, but switched to Sport, whose increased power and reduced nanny intrusion is easily noticed.
1: Erect seating posture makes you subject to vertical spine loads over any large bumps, like a cruiser seat, and the U-shaped seat give you no room to move around on the bike for comfort (monkey butt) or cornering.
2: Left handgrip computer controller takes some getting used to, and sometimes doesn't respond immediately to "clicks". Without the manual, it's not obvious how to adjust the ESA preload, just the damping.
All of those for the GTL, plus:
1: Seating position very slightly leaned forward with stock bars and seat, much more comfortable for me overall than GTL. Still more upright than my K1200GT, even with the K12's bars at the highest position. Seat itself is flatter and allows more fore-and-aft, as well as more sideways movement on the bike for comfort and cornering. Seat height is higher, but I could almost put feet flat along bike, at 5'11", with a 31" inseam. Seat is still softer and more comfortable than the K1200GT stock seat.
2: Handling is awesome for a bike of this weight, like the GTL but even moreso. It was very confidence-inspiring on the best fast twisty road in our area, at pretty high speeds.
3: Brakes are spectacular, and I could evaluate them more completely on this more sporting machine, as I could ride it harder and brake harder. Among the best I've ever ridden. Very strong, progressive, no fade ever. Linkage from front brake to rear is subtle and transparent to rider.
4: The windscreen gives good, not great protection from buffeting in its nearly top position for me, with a nice notch at the centerline that allowed me to look over the screen but still benefit from the greater protection overall. I was pretty warm behind the raised screen on the 86 degree F. day I rode the GT on, almost too protected. Moderate helmet buffeting at speed with screen lowered, but I liked it best in that position for spirited riding on a twisty road.
As on the GTL as far as handgrip, but not seating, and:
1: A little more radiant heat on my feet, L > R, was noticeable on the warm day I tested the GT. It seemed to be coming from the header pipes, which are in the airstream just in front and below the pegs. Not awful but some sort of deflector at the lower edge of the fairing between the headers and the pegs would help this, I think.
2: The front of the seat is a little wide, so standing on ground astride the bike is a little uncomfortable for long periods.
Overall, I really liked both bikes, but I liked the GT a little more for my riding style and ergonomic preferences. YMMV, of course. I think the greater agility, better ergonomics, and the smoother power with no vibration are both bikes main advantages over the K1200GT. I am now on the list for a GT after the pre-release ordered bike deliveries are done. I'm looking forward to it.