This looks like a good first step to me - do you think we can adopt more of your previously proposed improvements?

Not sure there's much more to do unless we want to change functionality, which isn't compelling. But let me know if you got ideas and we can iterate. Thanks for your help with this @ioquatix!

As a bonus, it looks like we inspired Rails to clean up their usage of Singleton! 🙌🏻 🧹

What I would suggest, is reopening a draft PR with your proposed changes, and just let it sit for until Rails 7.x is EOL, then we can merge it.

I'm sure any tests that you wrote would also be welcome.

The fact that rails deliberately re-introduced .new in a singleton class is clearly a misuse of the singleton pattern and I liked your simplifications, so we shouldn't let that prevent future adoption.