If you buy a Tesla today, Full Self Driving costs $3000 now but $4000 later. If you know you'll buy it when it's available, the point at which it becomes viable along with the return on an alternative investment determines whether it's better to buy now or later. For example, if after taxes you can make 7% annually elsewhere, it would be better to buy now assuming FSD is available in fewer than 4 years, since your $3000 would be worth only $3932 in 4 years. Now the question is: when do you think it will actually be available? And no, the answer isn't "3 months maybe, 6 months definitely".