I think that they missed the boat with that presumption. Kids could afford records, maybe not much equipment yet. I know I was one! Within a few short years those "kids" would be affluent enough to afford quad equipement. The "experiment" was called off before being given half a chance. Most older folk were still happy with mono!
A lot of "hard rock" was released on Q8, I guess they figured that "kids" could afford those! Wait a minute, tapes were always more expensive than records!
But the playback hardware was easier and cheaper, esp in the car