sbt is not the only build tool that supports Scala.js. I at least know of support for Maven [1], Pants [2], Gradle [3] (a bit outdated that one, but an interested person could revive it), and there seems to be a path forward for Bazel [4].

That said, I would like to see a Webpack plugin for Scala.js as well.

[1] https://github.com/random-maven/scalor-maven-plugin [2] https://github.com/pantsbuild/pants/tree/master/contrib/scal... [3] https://github.com/gtache/scalajs-gradle [4]