From what I understand, one of the reasons why it's impractical to recover upper stages of rockets is that they're traveling at high speeds, and methods of making them bleed off that speed (such as heat shields) would make them too heavy.
However, would it be possible to reuse upper stages with a plasma magnet drive like the one discussed in the Centauri Dreams post The Plasma Magnet Drive: A Simple, Cheap Drive for the Solar System and Beyond? Essentially, this is an upgraded version of the M2P2 concept of magnetic sail. One of the proposed applications for this is to allow a spacecraft to land via aerobraking, without needing a heavy heat shield. If this is possible, then it should also be possible to land the stages of a rocket that's taking off.