One idea I’ve had related to storing digital data on tape is to make a mp3 cassette tape. So you could have something in like a walkman form factor, and put actual tape in it, but it’d store digit mp3 audio. Completely impractical but it’d be a great mashup of old and new(-ish)

old digital tape standards could store like 1.2Kb (not even kilo-bytes), but I wonder if with modern dsp techniques we could get it higher.

My napkin math says if tape has a bandwidth of about 10khz, and you could sample the tape with a 8bit dac at 10khz, then that would be 10KB/s, or about 36MB for a 60 minute tape, enough to store like maybe 10 minutes of medium quality music. If you dropped the bitrate of the mp3 down to 10KB/s then you’d even get the full 1 hour play time (I just hope you don’t like cymbals)

Don't forget that tape has 4 tracks (used as 2x stereo in traditional audio tape). Other experiments have used 1 track as a pilot town to correct for flutter, but that still leaves 3x as much bandwidth as you were assuming.

[edit]

Found one of the ones I was thinking of. They were able to get about 24kbps on a single track, with a pilot tone on the other track to correct for flutter. This would imply 72kbps if using all 4 tracks simultaneously. At that rate, you probably get better quality audio with Opus than you would storing on a tape without some form of NR, though you only get half as much playback time.

https://redfrontdoor.org/blog/?p=795