It would be pretty crazy to hack up SCI to support MP3. They're not just mouse support, or new pictures, they are complicated compressed files which take a lot of CPU to not only decode and play, but it would take an outrageous amount of code (as far a hacking is concerned) to implement them in an original interpreter. Writing an MP3 decoder in assembly language is one thing (it would be sooooo much code, and take ages to do), but actually combining the asm of the mp3 decoder and the original executable, and making them work together would be nuts.
Lars' audio cd suggestion is an excellent idea! Remember guys, that SCI games do run without the audio (just without music), so people could still play the games if they didn't chose to burn anything. And if they did choose to burn them, it would be no trouble with good ISOs or BIN-CUEs along with the MP3s. That's exactly how SegaCD ISOs are distributed.
It may sound like a lot of work to create a game with all these ISOs/MP3s/get users to burn them and all, but if you think about it, Sierra's games with CD audio were mostly mega$$$ productions, so the effort of burning special CDs wasn't a big deal.
I personally think though, that most people woundn't be composing their own tunes, but rather, just be using existing copyrighted music, which could cause issues. And... if they're just using tunes from their favorite band's CD, it's probably not going to perfectly fit the atmosphere of the game, even if they both have the same message. A perfect example of music in a game is DOOM, where youv'e got all the ticking, and sound effects, and such, they really give a good feel to match the rest of the game. Besides, where's the classic 2D adventure game feeling if we match all the low-res graphics, simple sfx and simple interface with Britney Spears, hehe
