The nock takes a lot of stress, including sideways stress as the string rolls off the shooter's fingers. An inch longer nock, if made out of plastic, wouldn't be as strong as current set ups. Too, it might exert a sideways, splitting force on the arrow shaft, which could probably be overcome by making the inserted part of the nock longer.
The better solution would be to manufacture carbon arrows a little longer. Given that humans keep getting larger and commensurately our draw lengths, maybe some manufacturers will add a little length to their shafts in the future.
Of course, you can splice carbon, using an inner ferrule much like a fishing rod, but it's a lot of trouble to go through to add an inch of length.