One issue that Scala has been dealing with for ages is a "oh my god, look at these sharp edges, I'll hurt myself!" response. Even if an individual more or less trusts themselves to make good decisions about language constructs, there's the concern that an individual library can (or has) force inappropriate complexity on them.
Giving people a mechanism to limit, or at least easily discover, the use of complicated language features sounds like a PR win for Scala.
Except that I'm pretty sure he isn't denying that the language is complex. From Martin's comment, it appears that he is saying that Scala provides powerful and complex language features to solve hard problems, but that it isn't Scala's fault that people are so persistent about abusing them.
Then it's probably a good thing that no one was making that claim.
You may instead find people claiming that the complexity "isn't a problem" or "can be avoided by convention." I don't fully agree with either of those statements. A "complexity safety switch" (nice term, by the way) helps to alert programmers that more difficult language constructs are at play in a given piece of code. Identifying and advertising the use of problematic-but-useful language features seems like a good compromise between omitting them and allowing people to naively wander into them.
Giving people a mechanism to limit, or at least easily discover, the use of complicated language features sounds like a PR win for Scala.