At lot of people may disagree with this, but personally I'd love for cassette tapes to make a comeback, lol.
CD's spoiled me, but really... Looking back I HATE cassette tapes. Even more than I hate the restrictiveness of VHS. If you want to skip songs, you have to fast forward and rewind to get to the right spot... the sound gets pretty muddy when the tape gets old enough... and if there's a slight defect in either the tape or the machine, the player eats it up, pulling all that tape all over the place causing a big mess.
Records I can dig, but those players... I never was able to do it myself. My mom had to help me (I graduated to cassettes by the time I was 7), and thankfully, nothing was ever damaged to the point it was skipping. I have a whole bunch of Sesame Street albums I haven't heard in ages. But the one thing they have that no one else has? Big ol' wonderful covers with great designs. I wish there was a place that had high res scans of Sesame Street album covers I could make wall art out of.
Yeah, records have been "back" for a while, though every used record store I saw has gone under years ago. I almost bought a 45 single of a Dexter's Laboratory hip hop piece. No kidding. It was like 2 bucks too. Should have got it for the collector's value.