Right now at Yammer we're moving our basic infrastructure stack over to Java, and keeping Scala support around in the form of façades and legacy libraries.
The link you provided doesn't contradict that.
Language can be too simple or too complex. The tradeoff that gives maximum productivity is somewhere in the middle. And in my opinion, languages like Dart or Ceylon are much closer to the optimum than Scala.
I don't think you've done anything to substantiate the claim that it's "too complex"; forgive my skepticism but I've spent enough time in both the Scala and C++ communities to draw a significant line between "too complex" and "critic hasn't learned it sufficiently" (and I've been on both sides of that line).
I have spent a nontrivial amount of time with Kotlin and Ceylon and neither are particularly interesting to me after actually internalizing and understanding Scala; as an example, I am significantly hampered by their continued insistence on mutable-everywhere (which is basically the watchword for "barely adequate programmer"). They may very well be "the next Java", but that's a curse more than a compliment. You should not need Guava to write minimally competent code.
Meanwhile, as a sibling comment notes, Twitter's a lot bigger than Yammer and pretty vocal about going whole-hog on Scala (and I've talked to them a little about what they've done, it's insanely impressive, I'm jealous). Guess they're just making things hard on themselves for no reason though.
Linus Torvalds is in the C++ is too complex camp too AFAIK :)
I believe that Ceylon is the best-designed general purpose language out there. What do you mean by "mutable-everywhere"? Ceylon's variables / attributes are immutable by default.
The link you provided doesn't contradict that.
Language can be too simple or too complex. The tradeoff that gives maximum productivity is somewhere in the middle. And in my opinion, languages like Dart or Ceylon are much closer to the optimum than Scala.