ActivityGroup is itself a custom Activity - it inherits from Activity
If you want to add data-binding to any custom Activity, then you can do this using the event source and mvx steps similar to the steps described for ActionBarActivity
in: http://blog.ostebaronen.dk/2013/11/getting-support-v7-working-with.html
If you then want to introduce custom navigation then you can override the default MvvmCross presenter - see https://github.com/MvvmCross/MvvmCross/wiki/Customising-using-App-and-Setup#custom-presenters and http://slodge.blogspot.co.uk/2013/06/presenter-roundup.html