In my experience in Cambodia and Thailand (and I would fully expect Laos to be the same), a Honda XR250 is about the best bike you can get. You can't kill it, and parts are available in Thailand if you ever do anything incredible to it.
Forget the KTM. I hate to say it, but forget it. Oh, and forget your BMW 1200R too. Man, I'd be pissed to have my GS in Cambodia unless I was just "riding through." ALL of the backroads are dirt, which is fine, but there are so many potholes it is like craters of the moon. A WR250 (not the R like I have, but a real one) would be even better.
Enough power to lift the front when you are jumping potholes.
Good source of knobbies
If it's that, you can do all sorts of hellacious riding.
My TAT trip will hopefully bring more attention to the need for more Cancer Research! Please go to http://www.gofundme.com/bxkt74 and check it out! No money goes to me or family, all to cancer research! Please donate at the location!!! Thanks!