You might actually be a few years behind the curve.

http://www.re-filament.com

We've had access to 3D printing with filament made from recycled plastic waste for a little bit now. There are some problems with it, in part the fact that it is a long way from efficient process, that the degradation in the quality of the plastic having been processed once means that you have to mix in a fair quantity of un-recycled plastic, and the whole process is just way more expensive than it really needs to be to become truly widespread.

But it already exists.

Whether it might ever become a truly useful technology – that's a whole different question which probably ought not to be left to blue sky speculation.