Note that it’s not necessarily a valid assumption that $4000 for after market activation of FSD will stay at that price, or even be offered in the future. Tesla routinely tweaks those prices or makes certain upgrades disappear...I get that this is a hyperbolic twist on the Elon joke from the OP, but let’s say we take it at face value and do the math. In 3 years you’d be better off buying FSD now if you could get up to 10% on your money annually elsewhere, and in 5 years you’d be better off at up to nearly 5%. $3000 * 1.1^3 = $3993, $3000 * 1.1^5 = $4020.
AP1’s aftermarket activation price went up for everyone when they bumped the price of the option.