Dude.
I want
this.
I wonder if I could make one? Hmm... I mean, it looks like it essentially works like a bicycle, really, with the gears at least, you're just transfering the motion from the treadmill to the axles... I think the Boy knows how properly to solder things, and I'm sure the equipment needed is at school somewhere.... I'm much too interested in making something like this, let me tell you right now.
In fact... I wonder what it'd take to make it work all seasons? Snowtires, maybe? Much easier to carry an umbrella while walking than biking, for example. You could even make a removable top for it, something making use of bendypoles like tents have...
Places that were too far away to walk to suddenly wouldn't be, because you'd only be walking part of the way. You could probably lock it up like a bike. If the handlebars could fold down at treadmill level (very carefully designed not to happen accidentally, obviously) then it would fold flattish and be simple to store....