First EAP of renewed Scala plugin for Diana (IDEA 8) can be downloaded now from our plugin repository (see http://plugins.intellij.net/plugin/?id=1347).
By time of this message we implemented common go-to functionalities, structure view for Scala files, support for Scala SDK and basic completion and resolve functionalities for keywords, local variables and classes. There is no special run configuration, Scala applications can bu launched as common Java applications.
To use this plugin you must have Diana EAP (available at http://www.jetbrains.net/confluence/display/IDEADEV/Diana+EAP) and Scala SDK (see http://www.scala-lang.org/downloads/).
We wait for your comments and observations.