Karate Monkey?

It has Breezer-style track ends, but Burley makes an alternative hitch for either skewered or nutted hubs with those.

Sheldon "Nothing Exceeds Like Excess" Brown built one with both drop & straight bars & disc & cantilever brakes, but certainly road-style tires & saddle.

Also- more money, but eccentric BB instead of track ends is the Tout Boulevard.
$1200 for the frameset.

I looked for Paragon or Rohloff sliding dropouts & found them awfully rare on production bikes. Gunnar makes a MTB with Paragon, but if you want to avoid the torque arm, it seems like custom is the only option-- am I missing something?