Correction...unlikely anytime in the near future.

But eventually the oil will start to run out for real...at that point larger airplanes really are more cost-effective. Frequency will be trumped by price and you will have 777 doing LAX-SFO...on Mon/WED/FRI/SUN. Unless a cost-effective Jet A alternative is available in mass-production quantities, airplanes will start to disappear, smallest ones first. When? Who knows for sure...but sometime this century and I suspect somewhat sooner rather than later.