Let us purchase upgrades
In the model 3, partial premium interior vehicles, let us purchase premium connectivity and also let us pay to get the A pillar and door tweeter speakers activated. While you are there, why not let us pay to get ambient lighting turned on also.
Charge a monthly or a yearly price and lot's of people will be willing to pay to get those small upgrades. The hardware is already there, so why not use it to get some extra income for previously sold vehicles.
A lot of income potential for tesla without any extra hardware cost? This is a no brainer!