If you give them a software feature that can only be bought once, there's no way they will ever pay for it because they already have it.
Fine, charge them something fair for future upgrades but don’t disavow the entire FSD software package that they purchased (option to use it when it actually becomes available), with the release date of FSD getting constantly pushed off.
Tesla could be making a fortune by selling lane change additions to AP. This feature is fully functional now. Sell that!