"foo".asSequence() works fine. I understood your long hypothetical conversation: you want to avoid an intermediary method that returns a collection of chars. I just fail to see why anyone would care about this.
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...
At any rate, you never addressed the core point I raised. Saying "implicit resolution isn't related to implicit classes" doesn't seem very convincing. If solving that issue was so easy then why is the use of implicits so frequently identified as a performance issue for tools?