I really like your logic John, but i don't think that because of this you won't be able to use this feature. I don't know the operation of every shopping carts, but i doupt that any of them would fulfill this need. Of course it is possible, but i think only if you were involved into the software designing process.
I believe that coupons are mostly use while promoting your store and the word discount is almost equal to the word FREE, so it will attract visitors to your site. Don't get me wrong i see your point, but transferring the script to manage this kind of logic would be a great issue. Currently we spend most of our time on testing the new script which will help us to step further. Soon the
Premium Boss Cart will be ready to go to public and when the supporting issues will let me to go back to JV i will compile your ideas, because all of them is fantastic, and will try to do my very best, i promise!
Cheers
Bagi