Once again, the issue is covering the cost of such a thing. Okay, starting this year, NDK is going to be capped at 7,000 attendees, plus daily passes. This means you would need a minimum of 7,000 bags. The cost of covering the bags would most likely be our (the attendees) responsibility. Now, it is a possibility that along with t-shirts, pins and lanyards, the NDK staff could offer to sell official totes or messenger bags, but I doubt the cost of that would be cheap.
Now, don't get me wrong, I think the idea of reuseable bags is a great idea. But I also think that's something that falls under an individual responsibility. Bring your own totes, tell the people at the Dealers Room or Artist Alley that you don't need your purchase bagged, USE THE RECYCLE bin in your room.
As far as canvas bags cutting down on garbage at the convention, well you also have to realize you the tons of garbage generated by food and drinks. boxes of pocky, ramune bottles, bags of fast food, bottles of soda, starbucks coffee cups, food containers, etc etc.