Ive pondered on the idea as well but there was a warning about ds 520 and 400s back when they first came out. I believe it was something about 5th and 6th gears being 2 weak for the loads. They backed the theory by saying they are rfs 4st. other words racing four strokes.
I wouldnt steer clear from the street just not at highway speeds. i would use it to jump from one trail 2thanext if they are only a few miles at the most apart.
The ktm 525 would be my choice of a new bike but dont get one to cruise the streets.
I too am looking into a 525 dual sport. I know of a few locally and they all seem to be doing well. I did post a question in the thumper forum about valve train reliability. It seems there is a fix for the older bikes and I assume the newer ones are good to go right outa the box.
I have ridden the 520 on the street and it does quite well. However the revs seem a little high for fast roads. I know the bike will top 100MPH in stock form, yet the gearing is still not ideal for the street.
I can think of no other bike more worthy of dual sport conversion.
the clutch basket and rear sprocket are not dampened at all this combined with added traction of road riding would prematurely wear 5 and 6 gear as well as others 5 and 6 are thinner narrower there for are not made to handle the torque load implied