Clearly it is easiest for a Java or .NET developer to learn Scala. For other communities, the stumbling blocks don't have so much to do with the language itself as with the way we package it and the way the tools are set up, which is Java specific. Once they learn how these things are set up, it should not be hard to learn the language itself.
I'd already come to this conclusion on my own, as someone who has never used Java and is trying to guess at the Java conventions needed for Scala. I think this is typical of newer languages: you can't easily learn them without knowing a specific other language already.