There's nothing "shaky" about Scala's complexity, it's quite stable, and not going anywhere until Dotty lands circa 2020.
Despite everything (slow compiler, average tooling, implicit/operator overloaded "magic" code bases, etc.) Scala will draw library creators (like those behind Spark, Kafka, Akka, Play, etc.) which in turn draws developers, resulting in the thriving ecosystem backing the language.
Scala will live on despite itself; the ecosystem is what will carry the language to the Dotty land and beyond.
First, IntelliJ is quite decent nowadays. So it's demonstrably possible to build a decent IDE for Scala.
Second, Eclipse itself has imploded in my opinion. Eclipse used to be a usable and reasonably fast IDE. Then, some years ago, there was noticeable increase in bloat and a downgraded performance for Java. I remember reading some major release of Eclipse, which required a refactor of its UI, didn't have any automated tests because the refactor broke them and there was a lack of volunteers willing to fix the tests. Nowadays I've stopped using Eclipse even for Java, because I cannot stand its slowness and random freezing/crashes.