Dave_K has hit it on the head. It's not that I have a problem with getting games. I already have a decent library of good dreamcast games, but I want my arcade cabinet to be an arcade. I like guests to be able to walk up to it and choose what they want to play, a la MAME.
I also haven't hacked any controllers, and would just as soon not, if I don't have to. I guess the N64 emulators, and to a lesser degree the PSX emulators appeared so fast that it seems to me that Dreamcast would have been done by now.
Regarding hacking a Dreamcast with a CD changer, that's not even an idea I would entertain, let alone a project I would undertake. My skill levels, from electronics, to the programming that would be required, are not even remotely close to what they would need to be to come close to success with a project like that.