Interesting shape and theory about eradication of prop wash. 
I did see that - I think this is likely true in the context of racing (those guys are very much into it) - in fast fwd flight, to move the rear props away from the front props dirty air.
I cannot imagine it solves the issue if you intentionally drop into your own dirty air.
I thought the “old” DJI FPV drone had the rear motors above the front?
I would not know as I am way too young 
It rings a bell but I cannot find any pic of it tbh - the DJI FPV pics I find seem setup in a traditional manner but they may not be the same version you are referring to.
I did see something similar done a few years ago with small-ish printed frame but not seen it tried like this by professional racers. They launched it just ahead of a big racing event so results will tell if they find any advantages with this design.