Would LEGO use recycled plastic?
The LEGO Group has already created clear sustainability goals.

TLG is currently investing money to try to find sustainable and non-petroleum based ways to design LEGO bricks. Here's some info about the new Sustainable Materials Center that TLG is working on:

http://www.lego.com/en-us/aboutus/news-room/2015/june/sustainable-materials-centre

It sounds like they are investing significant money (1 billion DKK, ~150 million USD) and manpower (100 new employees) into solving this problem. They have also made it clear that they want to keep their focus on product quality while exploring sustainable technologies, so it sounds like whatever new plastics they develop will need to be at least as high quality as ABS.

If you are interested in collaborating with them on this, you'll need to get in touch with TLG directly. This is a fan-moderated FAQ site, so you are unlikely to get a response from a LEGO employee. I'd recommend using the "Contact Us" page on LEGO.com.