Metric please! My number one would be make all the bolts and nuts metric. Virtually all the bikes on which we run these kits are metric and carrying two sets of tools doesn't make sense. Just doing that would equal a bit of weight savings by our not having to carry extra tools and save, at least for me, some frustration. Owning ATVs, snowmobiles, cars, motorcycles, etc and this being the only item that is not metric, it bugs me everytime I have to pull out the never-used SAE tools. Ha. So do away with SAE and go metric like everything else we own.
The rest of these have been mentioned already, but just to give another vote...
Use bolts that are of the proper configuration so the shank is the correct length and the threads aren't contacting and wallowing out the mounting hole.
Clearance for longer paddles and/or offer longer tracks with bigger paddles directly on the new kits.
I don't care about weight reduction near as much as reliability. Do whatever it takes, even if it adds a bit of weight, to make the kit more robust to minor hits and flexing. Reduced flexing would help keep everything aligned better and potentially head off wear issues with bearings, sprockets, and everything in between.
Enclose entire tunnel to keep snow off back of engine, rider and brake.
Splined shafts for sprockets rather than key ways. Not sure why, but splines just seem more secure and robust. Probably my imagination and I haven't had any probs with keyways, so mark this one as very low priority on the wish list because the extra cost on this one probably makes it not worth it.
Reduced price would be nice but the above improvements are way more important to me and worth paying for in my book. Regarding price and getting people into the sport, there are enough used kits trickling down so those that don't want to spend as much can get into the sport. No different from sleds or cars or whatever. We all want this years sled, but want to pay what a 5 year old used one costs. Ha. So, keep focusing on improvements and quality and let the price fall where it may. Someone will always come up with a cheaper kit with inferior quality but most will still see the value in quality. More than likely any price reduction will come from volume efficiencies by making more kits each season as the sport grows and/or buying raw materials or components in a larger volume as more and more people buy the kits.