Why not?
The first stage is just a re-hash of the old Saturn S-IVB stage recoverability concepts and If SpaceX can develop sufficiently reliable engines why not use 'em to land?
Watch closely - the rocket lifts off from the cape, boosts second stage to serious speed, then suddenly lands back at the cape.
So, it should either go around an orbit, making the whole thing an SSTO and second stage redundant.
Or brake, accelerate back, brake again, making the whole thing pretty much a double SSTO.
What other options are there?