The pull request has been closed with a remark implying that it’s currently not in focus.
Personally, I think it’s a mistake to release Scala 3 without a built-in effect system. People will continue to rely on things like custom monad stacks and for-comprehensions to emulate one, which leads to horrible looking code that is hard to understand and even harder to edit. Or they go out of their way to create prettier but incomplete solutions that are even less well supported.
In fact, depending on how you look at it, because it lacks a proper effect system Scala is currently a less type-safe language than Java in that Java at least has checked exceptions whereas in Scala anything can throw at any time without it showing up in the types.