The problem is already with us; see the increasingly difficult economics of 32-to 50-seater regional jets such as the Do328 Jet, EMB-135/145, CRJ100/200, etc. with a fuel price of US$ 60/barrel... Sooner or later, the problem will extend to the still popular 70-seaters (CRJ700, ERJ 170).
The recent upsurge in orders for more fuel-efficient aircraft such as the ATR42/72-500 is further proof.
Fuel costs are bound to replace wages as the no.1 cost for airlines in the medium term.
(As for trains needing to be electric-powered, that has been obvious for a long time overseas: in France, one can hardly find any fossil-fuel powered train anymore; they are nearly all electric powered - which means nuclear-powered in the French case).
Cheers
