Don't know about Kotlin, but Scala and Xtend are two very different beasts.
Contrary to common sayings, Scala is NOT a better Java. Scala is much more featured language than Java, with its own syntax and semantics, and its own pack of base libraries.
Xtend IS a better Java. It keeps Java semantics and enhances its syntax. Every line of Xtend code can be directly translated to a bunch of java lines of code. There's no additional runtime, neither.
I think that both approaches are right, although different. I don't dislike Scala (as a language), but don't like having Scala jars added to my projects. I can't use Scala properly in Android, neither (it adds weight and performance issues). Xtend is not as much featured, but it's Ok for me (much worth using it than Java language) and it works on every platform as if I were writing directly in Java.
I believe both languages cover different niches and can coexist without interferring one to each other. IMHO, Scala is just too complex, adding nothing new. Iif you want to go more functional and less OO, just pick one of many simpler functional languages, like Clojure or JHaskell. If you just want Java with some better syntax and a bit of functional programming, Fantom would be as great as Scala (it resembles C# a lot).
But I find Xtend being in a sweet point in between all those languages. It adds all those syntactic patterns I wanted for Java, keeping the good parts of Java (its semantics). Think about it as Coffescript for Java.
And Eclipse support is superb...