The Kotlin guys are very against implicits. Everything in Kotlin is explicit. Even a conversion from Int to Long has to be done explicity. Scala's implicits are one of the major culprits for long compilation times. I once wrote an article about it: https://dzone.com/articles/implicits-scala-conversion. Then they are a real problem for code readability if over used. There was once a thread on Scala's user group where someone was asking for a special debugger to debug what implicit conversions are happening at runtime to better understand what is going on after compile time. Unhappily, I didn't note down the link, but you should be able to google it. Several people replied and said this would seem a good idea to them and this really scared me. My understanding of Scala is nevertheless not sufficient to say how problematic implicits really are. As I understand it they are mostly needed to create the blend of OOP and FP. If you are not heavily into FP like the Kotlin guys (There is a remark by Andrey Breslav saying something similar to this: "FP solves many problems easily, sometimes at a high price") implicits is not something you need. And I don't think they were a good idea in Scala to begin with.
– Oliver