Yeah, we can think about this. Thanks for the link.
Honestly, this is the first request we've had related to co2 emissions. I'm not positive it's an important aspect to people yet. Maybe it is outside the US? When I get together with friends and family we always talk MPG, not emissions. But I do think it's something we could potentially help people think about.
Emissions are important in the UK because we pay road tax, which is based on the emissions. Low emitting cars are free! But something like a Jeep for example would cost you something like $600 a year in road tax, even if you don't use the car. Then our fuel is almost $10 a gallon, you can see why we tend to drive smaller more economical cars!
Perhaps a way of monetizing this functionality, is that you could integrate with 3rd party off-setting programs and take a cut (for those people interested in offsetting their driving emissions). Just a thought.