I use a pd-8x on my MTB, and sometimes I have to augment it with a battery light. I'm really slow on a mtb. Also, most dyno lights don't have quite a wide enough beam to work well on twisty singletrack. But I think most mtb-ers use a helmet light because no fixed headlight works that well on twisty singletrack.

My lbs got a SON hub for someone's pugsley, and ordered the wrong one, so they had to get a second one.

My SON is 150mm, so I guess you can't adapt that model to a pugsley without going to a TA fork.