Some F6B Riders as well as some 1800 Wingers are going darkside. I haven't been around an 1800 Valk to check it out, but if it works on the other two I would guess it would be doable on the Valk. One thing though, I don't think they are going with as wide of a tire as the 1500 riders.
I see the new Valk rear is 17" ??? and the wing and 1500's are 16" that might b a game changer. I run DS on both of my 1500 I/S.