A mobile treadmill sounds about like the apex of idiocy that a techological society could possibly reach. I mean, you're basically walking on a big, hundred pound hunk of steel so that you can, well...walk. Kind of overengineered considering that you have a pair of legs that can do that for you. And if you don't have a pair of legs, you can't really walk on a rolling treadmill either. It's just begging for a Polish joke.
Currently in prototype phase at Waseda University in Tokyo, Japan, the Tread-Walker does provide some benefit. Those crafty Japanese are too clever to create a treadmill that just translates your foot steps into comparable motion; the Tread-Walk is designed to amplify steps by 1.5 to 3 x to give you a little more oomph for your input. It's being created as a means for the elderly and disabled to walk around freely.
Users can control the speed via an "active speed control." Like a bike or scooter, the handlebars provide seamless maneuverability.
It still looks like it'd be a bit large and expensive for the minimal boost that it will provide (I'd think you'd be better off with a scooter or even a dreaded Segway). However, if it lets folks that are barred from mobility gain more freedom and enjoy access to healthy exercise, than it seems like a noble endeavor. According to the video presentation, 80 percent of those that have taken it for a spin have had a positive reaction.
Hopefully, they'll be able to shrink it down, if they ever aim to get it to market.
Watch it in action in the video below; it's actually quite interesting to see.