Ideally, I think I'd want a singular container (of whatever sort) that has the album's audio, the music-related timing metadata (as applicable), and whatever other metadata may be appropriate (lyrics? liner note graphics? music videos? sure!).
The audio should be able to be FLAC. But it should also be able to be anything else, like Vorbis or MP3 or AAC or IDK. It needs to be able to be played continuously without aberration (which can't actually be done with a group of MP3 streams).
The audio needs to be able to be seekable, like a CD is also seekable. By track. By index. (With pregaps, where appropriate -- because CDs also have pregaps.)
Other potential metadata must be able to include whatever subcodes are involved in things like CD+G[0] and HDCD and CD Text, since all of those are supersets of the regular datastream and playback is compatible with any CD player.
And it needs to be a singular container file because...well, that's just easier to keep track of as the years go by and data migrates.
Only then, will we have the beginning of a valid archive format for audio CDs as they actually still exist on [some] store shelves today.
(Some stuff can be optional, just as lots of things are optional inside of an MKV container for a film.)
[0]: Almost nobody ever used this outside of the 1990s karaoke world, but Information Society's self-titled album includes an illustrated sequence, with lyrics, that is completely implemented in CD+G and that runs for the entire length of the album. And I should be able to render that locally here in 2024 from a container on my pocket supercomputer instead of watching a bad rip from a Sega Genesis: https://www.youtube.com/watch?v=b89sSa8QlLg