Having a subscription might make people run agents overnight, or casually generate images for fun, or start more coding projects. The reason gym memberships work is that people like the idea of going to the gym a lot but don't really enjoy actually doing it very much and fall off over time, leaving the gym for the rare person who's really into fitness to use it cheaply.
is AI like that where most users will get bored? or is it like movies where they'll try to get their money's worth?
User's getting bored will also spell trouble for the subscription model. I don't think we'll see a world where the average normie is going to be running agents in a loop overnight to make software. They'll get bored use it to cheat on their homework and as a Google replacement, generate silly images for a week then get bored of that, and then realize the have no actual reason to be spending $100/month and drop down to a lower tier or just cancel all together and live within the free-tier limits.
So if that happens, the labs are now left only with power users that can actually generate asymmetric cost. The market will bifurcate into free-tier users and "get their money's worth" users. So the risk isn't that the top 5% of users use more tokens than the subscription has any right to give you, it's that everyone else cancels their plans and only those top 5% of users remain.
The labs will have to put stricter rate limiting and token limits on the subscription plans to avoid MoviePass style burn.
Gyms get away with it because most don't let you cancel easily. You pay monthly, but are locked in for 6 months or a 1 year at a time (Adobe subscription style). Maybe the labs will start to do the same? Let you pay $20/month, but you are forced into an annual commitment?
Another point against your gym analogy. When people don't have that much disposable income why would they subscribe to something they semi regularly use? And if it becomes more expensive why would they not cancel it?
I don't see where the difference is with gym subscriptions here.
Especially if part two of your theory comes to fruition and they have to raise prices. I might of forgotten my Netflix subscription when it was 10 dollars a month but certainly not if it was 200 you know?