In "Scalazine" there are some articles about the Scala language, two of them are interesting:

"The Goals of Scala's Design", in particular the sections named "Object-oriented innovations in Scala" and "What's in it for me?":
http://www.artima.com/scalazine/articles/goals_of_scala.html

"The Purpose of Scala's Type System", especially the parts named "Existential types", "Variance in Java and Scala, and "Abstract type members":
http://www.artima.com/scalazine/articles/scalas_type_system.html

Some of that OOP and type system stuff may become useful for D.

Bye,
bearophile