Conceptually, with a 3mm chassis, a 1mm aluminum chassis guard would do the trick - but it would have to come that way. You can buy 4mm chassis, so the extra 1mm shouldn't be a big deal.
I wonder how that 7075 aluminum holds up. Quite a number of aftermaket companies offer it as chassis replacement. I'm sure it's not completely scratch free, but it must be better than what we're using now. Anybody got a 7075 chassis?
Does anybody know the long term impact of chassis scratches? If it's purely cosmetic, then it really seems futile to try and prevent scratching.
I was flipping through a magazine recently and saw that a few people painted the bottom of their chassis. It looked real nice, but I'm not sure how long it would last. Maybe you could just paint your chassis after every race?