You can already preset a next destination, so that covers a whole day's worth of movement, at worst, and up to a week's worth of travel.
Auto-pilot would dissuade people from logging in (at least daily), because "it'll be a while before I arrive anyways". It would also reduce interaction because people could just plot destination, and then not update the path along the way, because everyone else is already pre-set, forcing the military leaders to just go ahead with what was decided ahead of time.
I don't really see how this would be beneficial for inactive players anyways. If you miss a turn and start traveling late, auto-pilot won't give you back that lag time. It would remain the marshal's job to make sure the army doesn't spread over too many regions and, when it starts to stretch too much, issue a pause to let people catch up. Auto-pilot would even reduce his ability to issue pauses. And don't forget that many things can interrupt travel or affect travel times, and auto-pilot is likely to just make people less reactive to them. The guy with 10 cavalry, 5 scouts, and vanguard settings on auto-travel for hundreds of miles will likely arrive much faster than the guy who has 100 infantry, no scouts, and forgot to switch out of sentry mode, likely increasing the army stretch. If you miss 50% of your turns due to not logging in, then you'll still miss about 50% of the battles, because you didn't set travel on time. Auto-travel wouldn't improve this the least.
