Anyone ever tried this with an inexpensive old 3-speed hub? Just curious.
If you're talking an old 3-speed Sturmey-Archer AW, I would stay far, far away. Under 'normal' road conditions, the innards were known to wear and make them even more susceptible to non-perfect cable tension. Incorrect cable tension led to 'false-neutrals' between the gears - - usually at the most inopportune times (to the tune of much knee-banging, nut-busting and swearing boys who then got their mouths washed out with soap by their mothers).
There are modern IGHs that could prove worthy, have proper mountain bike hub-spacing (135mm) and even have disc brake mounts: Sturmey Archer XRK-8 (now made by SunRace in Taiwan) and a new disc brake Shimano Alfine. I think Dannihilator is messing around with an Alfine on his bike right now and finding it working well. Maybe he'll see this and enlighten us more.