I'm really on the fence about whether to pull the trigger or not. I'll be honest, I'm primarily interested in the technology (or novelty of it).
I plan to keep the car 10 years if it serves me well, so in the simplest sense, that's $67/month (straight line and yes, discounting opportunity cost). The subscription model is intriguing, but there are no details. Some have speculated it would be about 1/72 the cost of FSD, so about $111/mo at current pricing, jumping to $139/mo at next week's pricing. When FSD hits $12K or $15K, maybe $167 or $208/mo. I doubt the rate is going to be flat - especially if you can pop in and out of the plan. Maybe you can go month to month, or maybe you have to sign up for a year but pay monthly.
The other thing that occurs to me is if FSD should be thought of as an appreciating asset to the car. I buy it at $8K today and if I sell the car early (say in 3 years), my car has an option that may be selling for twice that (assuming competition doesn't drive prices down). Ah...Who knows?