At the same time you can still run a single $20 / month server for "smaller" apps even with Rails + Sidekiq + Action Cable + Postgres + Redis all running on the same server to power your solo developed SAAS app with thousands of customers while having a p95+ response time of <= 100ms.
PRs like this just mean things are going to get even better than they already are and is probably a precursor to converting a bunch of Rails internals to use Fibers over time. The best part about it is I as an end user don't need to know the details, I just know my CPU and memory usage will go down over time while runtime performance continues to get better than it already is.
I wonder how long it'll take before the pendulum swings so hard back into the direction of Rails that it shatters even the original growth spikes of Rails from all those years ago. With Hotwire Turbo being a thing now it's very possible to build very nice feeling apps without writing a ton of JS while leveraging good old HTML and HTTP with sprinkles of Stimulus and WebSockets.
The more I think about it, the more I talk myself into believing Ruby / Rails really are a once in a generation combination. It's truly that good for getting real shit done in a pleasant way.