Effect systems just arrived in languages beyond research. So it's no wonder that there is research like experimenting in the few real-world languages that try to implement an effect system. Nobody did implement it on a large scale until now!

Scala is mostly only including well known features. At least well known in the research space. Odersky does not experiment much, and is, I would say, actually quite "conservative" regarding language features.

This addition is quite innovative indeed. But there aren't much alternatives matching Scala's needs as this whole topic is quite "new" even in research, and just matured enough to be included in real-world languages. (Effect systems are about 20 years old; which is an age where ideas form research just start to surface beyond research for the first time. Most of Scala's other features—even those unknown to mainstream by the time Scala introduced them—were already tried out elsewhere and well know in contrast).

I'm really looking forward to this feature and hope it will make all the presented use-cases (and some more!) truly possible. Even if I still don't get the whole picture; as capture checking isn't really so useful on its own but instead a kind of enabler that needs to be combined with other features to unfold its whole potential. So I'm already very curious about the new patterns and emergent features capture checking will make possible in Scala which I didn't thought of until now.