I wouldn't say that it needs an IDE; it certainly does not need it any more than Java, C, C++ or Scala for that matter. But, it can certainly benefit from an IDE, and I don't think that such a language is flawed or even "flawed" by design. It's simply different.

I, too, am a fan of Clojure, but I'm also a fan of Java, and Kotlin is probably the language best called "a better Java". Both kinds of languages have their place.

And as for concurrency -- I'm not sure, but I suspect that it follows the Java/C++/Scala model rather than adopt an opinionated vision of concurrency like Clojure and Erlang do. But if you'd ever need to write a new concurrent data structure for use by your Clojure app, you'll be able to do that with Kotlin rather than Java.