FYI Tesla has already told regulators that it won't be able to deliver FSD by the end of 2021, which it had earlier committed to. If you are still holding your breath on it, it's probably time to give it up.
It’s a “loan” insofar the interest is paid out in over-the-air FSD updates and the principle is irrecoverable.
It's a cash payment to Tesla for a feature that doesn't yet exist, so technically they owe you something until they deliver FSD. If you bought this, you would have been owed $10k but in the form of a self-driving feature. So until they deliver that they technically owe you money, but they owe it to you in the form of FSD.