I really doubt that the math would tell Tesla there is more money in subscription. Most people would sign up at $100 a month, then drop it way before 80 months is up. Personally I would not pay more than a month (if that, having experienced AP and EAP), neither would my wife who keeps EAP2.5 disabled on her car. Even my 16 year old son tried EAP and doesn't like it either. We have AP1 and EAP2.5 on our Teslas, but AP1 is the only one which gets used (by me) from time to time. I try out out my wife's EAP as recently as a month ago (only on a highway), but it's still not as smooth as AP1, plus the phantom braking for no apparent reason just drove me nuts so I just turned it off. It wasn't tire screeching, accident causing slamming on the brakes, but still rather unpleasant slowdowns at highway speeds. Blind spot monitoring works better on EAP2.5 than AP1, I will give it that, not worth $8K though.
Notice that you can already get it $8K AP for ~$130 a month, just have to commit to 72 monthly payments up front. Let's see how many people sign up. A while back I polled some of my coworkers who bought Teslas, mostly Model 3's but there were a couple S's and one X, and majority did not pay for FSD even when it was $5K. Maybe Elon realized that the only people who will pay for FSD are not very price sensitive, so it makes sense to jack up the price - more money, same take rate of customers.