Yeah I'm pretty sure Elon said in an interview that the feature will inevitably become only available via subscription. Think about it from a car manufacturer's perspective. It isn't like cruise control where you build it, sell it, and you're done. This type of thing is going to require ongoing updates/refinements/etc. If you sell it to someone outright are you then obligated to continue to support it for the lifetime of that vehicle? What happens if a few years from now regulators decide that in order for a vehicle to be autonomous there needs to be specific piece of hardware (special radio transmitter lets say) in the car. Should Tesla pay for the install of it in everyone's car? It's a MASSIVE contingent liability and one that no company should reasonably be expected to shoulder.
Oh and if memory serves me right, someone tweeted Elon about transferring FSD to a new vehicle purchase and Elon responded saying they would look into it. So, that may be something that becomes possible down the road - but I don't see much financial incentive for them to pursue it.
Tesla got a little excited/greedy by doing exactly that when they sold the 'promise' of FSD. They've already had to upgrade all of the older computers at their cost when they determined the original hardware couldn't deliver on the promise. I've also seen whispers about new headlights with cameras, potentially required to see around corners when cross intersections. That may or may not be true - but the point is that until they have a completed product with regulatory approval anything can happen and right now they're technically on the hook to update customer's cars as needed.
10k is a lot, but arguably adds residual value to the vehicle. When the option to purchase it goes away, that should help bring the resale value of the option closer to what was paid (right now I estimate FSD adds 4-5k to the value of a used car). The RoboTaxi network is another interesting thing that could make the 10k investment a drop in the bucket - if it ever happens.
Finally, tons of people lease vehicles (especially luxury cars) and paying $10k for an option on a leased car (figure 5k deprecation of it per my comment above) over 36 months comes out to $140/month. A subscription may be a much better deal for people leasing.
The talk about the subscription has me slightly optimistic that a new more "true" version of FSD is on the horizon, as I can't imagine Tesla expect someone to pay a monthly subscription for it in its current state.
Finally - they're using it as a way to generate massive amounts of cash. If what I read about it is correct, they're not able to dip into the pool of cash completely but rather chip away at is as they release features closer and closer to what is promised. But, I'm pretty sure they found a workaround with the certified pre-owned program. Every CPO Tesla I've seen has FSD. They're taking cars as trade-ins, etc, and adding FSD and then turning around and re-selling them for the same, or in some cases, more than they sold them for new. I suspect in those instances the cash isn't being set aside but is immediately available.
Anyway that summarizes my thoughts on the entire scenario
cheers
Charlie