We are considering dropping support for Scala 2.11 in Scala.js core. Please upvote or downvote the GitHub issue, and comment if you have any (remaining) 2.11 use case.
I’m still using Scala.js with Scala 2.11 in one of my projects. But that’s a problem at my end (the project has gotten wedged due to a dependency that I need to disentangle), not at the language level. Upvoted.