I'm honestly a bit surprised that they went the route of making Autopilot cheaper instead of introducing a subscription based model. Charging $40/month over the course of 10 years, Tesla would get $4,800. The customer will like it more because they don't necessarily pay for the entire length of the Autopilot. So say someone buys a 3 and owns it for 4 years paying monthly, they only paid for the time they actually used the system($1,440). Then the next owner of the car can decide if they want to pay monthly for it. It's win for customers and Tesla gets long term monthly revenue.
I'd hate that. When I pay for something, it's supposed to be mine. If I choose not to pay the upgrade fee for the next version, it should still work. Because you never know what life will throw at you, having a bunch of "only $40/month" payments or your car doesn't work the way it did the previous month is not the way to financial security.