It's an interesting question as to why the purchase price has gone up significantly (from $10k to $12k and then to $15K) but the subscription price has not.
One theory is simply that they want to encourage the subscription revenue model.
Another theory (a hopeful one for those who purchased outright) is that Tesla has indeed decided that they will provide a no-charge hardware upgrade to those who purchased FSD, but not to those who subscribe. The increasing purchase price reflects this anticipated upgrade cost.
The FOMO argument in favor of purchasing vs. subscribing includes the ideas that
a) you'll get the hardware upgrade as mentioned above, and/or
b) the subscription price could be raised substantially at any time.
However, regarding a), as long as the subscription price remains the same, even a $5,000 charge for a hardware upgrade represents a wash vs. the original choice of $10k or $200/month.
Here I'm not expressing any opinion regarding the likelihood of various future Tesla actions, nor any advice regarding which FSD option (if any) is a better choice. I'm just trying to think it through and summarize the issues.
I bought FSD Capability at $10k. I'm not sorry I did, but I never tell others that's what they should do, even less so as the price has continued to rise. For me it had nothing to do with the concept of having a future income-generating Robotaxi; I always felt that was farfetched and not a particularly attractive1 use of my personal car.
Regarding a hardware upgrade, mostly I just hope it will be available at all for my car. Of course I'd prefer to be entitled to it at no further cost - but I have to admit I'd reluctantly pay for it. The worst outcome would be that it's simply not available even after buying FSD.