Hey I just like it when people do fun stuff that's all.
Well there's the issue of approaching the up sloping runway where the pilot feels they are high so will tend to fly a shallow approach and speed control can be a bit odd because you're not flying a normal approach. Then the flare is to a higher than normal nose attitude so he has to flare correctly using the far end of the runway as a reference. Losing the energy after landing is obviously greatly assisted by the upslope but if he gets too slow there's the possibility of stopping and rolling backwards which will never end well - if you're lucky it will end up sitting on its tail..
Taking off there will be a tendency to rotate to the normal cues given by the horizon which won't be good because that would be likely to biff the tail. Gaining enough speed to fly won't be tough because of the slope so leaving it on the mains until well after Vr and even V2 will mean much less rotation is required to make it fly so the chances of a tailstrike are less.
Realistic problems are how on earth do you calculate a V1, I've got no idea because once it's charging off down the hill I doubt anything would stop it so I suspect V1 was walking pace. I would fly if it fell of the end of the runway if you stuck the nose down!
Never done it, wish I had the money to buy a CJ or a 500 and go and do stuff like that and chuck the rules out of the window because I think everyone will admit, seeing slightly crazy stuff done in planes is pretty cool. I strongly suspect that although its miles outside the flight manual, the pilot has put an awful lot more thought and experience into it than some suspect. Which is normally true of people doing unusual things in planes where there is a successful outcome.
I've decided that Lundy is too short..