LLM subscriptions are not "all you can eat," they have rate limits — and fundamentally there is no difference between subscription-with-rate-limit and typical usage-based business practices. Subscriptions are simply usage-based pricing with volume discounts in exchange for upfront payment; every single usage-based provider of pretty much anything offers the same kind of discounting for buying volume commitments upfront. Although from a business sense, subscriptions are even better than volume discounts... Because they're recurring, whereas reserved volume might not recur.
Subscriptions aren't gonna go away. They're great for businesses. Rate limits or pricing might change but the underlying business model is very good.
The reason usage-based is so much more expensive than subscription isn't that usage-based is the "true" cost and subscription is a loss leader — just like a buying 30 consecutive day passes to a gym being more expensive than a monthly membership isn't a result of memberships being a loss leader. Memberships are the business model! The day passes are overpriced to steer you into buying the membership.
In the future LLMs will be priced per token, not all-you-can-eat.