Though in all honesty, Lego is Lego because it's made of quality plastics. I have Legos that I played with and young nephews are now playing with them. On top of that, new Legos fit with the old ones. This toy is being used for 30 years and it will continue to do so for decades. I can't think of any other toy that could be called more sustainable and timeless than Lego.
Since they're using ABS they have done some experiments with using recycled plastic. I think the biggest challenge is to get the quality to their standard. I don't think they made any pledges (didn't bother to check either) but they are at least testing the waters!