Pffft .... no big deal having a steep runway.
Fane in Papua New Guinea, averages about 12° slope and the middle is about 15° I think. Yes it's a one-way strip but because it's close to the equator there's never much wind so you don't have to suffer much head/tail at any time. The 2,000' drop at the end also does wonders to help build up airspeed if needed.
I can see how the idea of an inclined runway could work, but it'd be very difficult to work in the real world, with varying winds and so on.