I'm not trying to be an asshole, but I think it's a terrible idea that shouldn't come to be. I don't mind people that do it for themselves and keep track of what is original and what isn't. But anything more than for yourself I have a problem with.

First off, you would be doing this service and making some (even if nominal) profit off of Nintendo's property. I'm pretty sure that's illegal. Regardless, the main problem I have is that it is really just trash you are pasting on your cartridge, tainting the cart with something that shouldn't be there. (RevQuixo said it best in his post). I see it the same as someone losing their Halo game disc and replacing it with a DVD-R backup.

The last thing I want is to have to watch out for and worry about buying games with reproduction labels.

Something I wouldn't mind however, would be completely original labels using new art that didn't resemble the original label, with "reproduction label" in decent sized letters on the label.