Some context - the lead developer on the Scala Compiler, Paul Phillips, went slightly AWOL last year, and presented the talk "We're doing it all wrong" https://www.youtube.com/watch?v=TS1lpKBMkgg http://www.slideshare.net/extempore/keynote-pnw-scala-2013

He still seems slightly burnt by the whole thing: https://twitter.com/extempore2/status/493633548994097154

Other critiques of Scala collections have been made with the Typelevel library https://github.com/scalaz/scalaz which aims to fix these issues.

This post, 'Next Steps', seems to have come out of Martin Odersky's response to the situation. I commend him for taking practical and thought out action.