Check out this thread from the Black Ops Forum
This would definately be a popular idea
It wouldn't be too bad in some ways because you only have to make a few "unique" combinations and the rest are pretty much an average of the two guns unpgraded. I could see it working out and being really interesting until (not saying it wouldn't be fun for a long time) people figure out the limited combos. What would be awesome is if all the guns had a "unique" combo and maybe only 20 or so combinations were chosen to be used (at random) each game. This way you would have a small chance at getting a truly awesome gun and if you didn't it would extend playability.