I know many have done this to one, maybe two cartridges and so have I. My project began the moment my GameAxe (portable Famciom) arrived and I was bored with my old collection of games. Since then, I have come up with a Famicom cart for all mapper 3 games (CNROM) and mapper 1 (SNROM/MMC1) but only with some 128k games. NES carts are well documented however so I am changing my project to that field.
I am looking to recruit some motivated people to join me in creating documents on how to create NES host carts for mappers 0, 1, 2, 3, 4, 7, and even 11 if I can get enough people. In terms of horizonal/vertical mirroring on games, a jumper point shouldn't be terribly difficult to create on those games that don't have one built in. I'm prepared to supply anyone interested with all the documents and utilities they should need to make a cart that supports 1 mapper, at least 1 size combination of PRG and CHR ROMs, and 1 H/V switch if lucky. You will need the tools and skills to safely remove the ROM chips from your game(s) and possibly a RAM chip because you will have to trace exactly where the pins go from the ROM pinholes. Rewiring will always be involved but if it works in the end then that is a pretty big deal.
Anyways, if you're interested, email me at opieant@dominomail.com . If you have any cartridges you're willing to donate to this project but won't be able to partake in everything, email me as well so that I can tell you if they are useful or not. I'll be anxious to hear from people and hope that no one decides to be jerks and shun this project because it sounds stupid to them. Thanks people =)
PS. I plan to get my domain back up this evening so you can periodically check www.opieant.com for some sign of life.