Well, theoretically, "an Audio CD that exploits a buffer overflow of your music player on your computer and installs malware" is always a possibility, and a good intellectual challenge.

But doing it at an industrial scale and including an 0day exploit in all albums is a separate thing, I don't believe it would ever happen. On the other hand, creating an extension of the standard to "make a better CD" is a real threat, for example, a plausible example would be:

"a CD-based service that connects to a server to obtain metadata and lyrics of your music, like a proprietary version of MusicBrainz, but with ads and tracking added."