The wiki pages still say Daffodil requires scala version 2.9.x but we've upgraded to Scala 2.10 with DFDL-701. Following are locations where I saw the version mentioned but there could be more.

'Scala 2.9.2' (Under "Requirements") - https://opensource.ncsa.illinois.edu/confluence/display/DFDL/Getting+Started+for+Developers

'IMPORTANT: We are targeting Scala 2.9.x' and 'Because we are currently targeting Scala 2.9.x you will want to paste the following URL into the "work with:" box on the "Installing New Software" dialog: http://download.scala-ide.org/sdk/e37/*scala29*/stable/site' - https://opensource.ncsa.illinois.edu/confluence/display/DFDL/Configure+Eclipse%3A+Linux

'IMPORTANT: We are targeting Scala 2.9.x' and 'Because we are currently targeting Scala 2.9.x you will want to paste the following URL into the "work with:" box on the "Installing New Software" dialog: http://download.scala-ide.org/sdk/e37/*scala29*/stable/site' - https://opensource.ncsa.illinois.edu/confluence/display/DFDL/Configure+Eclipse%3A+Windows