No, I don't think you understood it. There is a large qualitative gap between what you propose, and what Scala does:

In Scala, it is an _one_ time effort to make String act "like" collections, while the only solution Kotlin provides means doing the work manually _n_ times: At every call site of the string in question.

Kotlin developers also didn't feel like your point was too convincing: https://github.com/JetBrains/kotlin/blob/master/libraries/st...