This is a really, really good question.
While Tesla believes the AP 2.0 hardware will be capable enough to achieve FSD, they have stated FSD is contingent upon passing validation testing (which Tesla is confident will happen) and in getting regulatory approval, which may require additional hardware.
This is why Tesla should modify their FSD purchase option.
Someone purchasing FSD with the car should be guaranteed that Tesla will make whatever hardware and software upgrades are required to allow FSD to be used in the car.
For owners waiting to upgrade later, the upgrade price should not be guaranteed. Initially the upgrade price could be low (like it is listed on the order page today). But if Tesla finds additional hardware upgrades are needed, then the upgrade price should be increased to cover the cost of those retrofits.
If V2V communication hardware is needed, then anyone ordering FSD now should get that for free. And anyone that waits to activate FSD should be expected to pay for that additional hardware.
Getting regulatory approval to enable FSD - and resolving the liability issues (so that Tesla will not be held liable for any accidents while the car is operating in FSD mode) could require hardware changes - and Tesla really hasn't addressed that in how they are framing the FSD option on the order page.