Two quick points in reply:
1) Coming down on the older 2-strokes, which will disappear on their own over time in compliance with the second law of thermodynamics and which are owned mostly if not exclusively by private anglers, will enrage an already hostile public as pandering to and accommodating the commercial sportfishery (read "guides"), and 2) Alaska Department of Environmental Conservation folks say that a 4-stroke emits about 75% of what a comparable 2-stroke does. Not a lot of difference. . .