[jayrot]

It would be a significant time investment to be checked out in a radically different type like this, but not impossible. It mostly comes down to the systems, avionics, and procedures which can be radically different already, even in similar-looking planes.

[8draco8]

I also wonder about engine placement. Engines on top will push the nose downwards in case of adding more trust. There is also issue of stalling on ascend. On ascend, wings would very easily obstruct air going into engines, reducing their power. Also currently aft-mounted engines require vertical stabilizer to be above them to counter act the forces generated by the engines. I don't see any vertical stabilizers in this concept.