There are a couple abilities left that still benefit Battle Brother Allies. They are mostly from the new Psychic Powers in the main rulebook. But they seem to be systematically removing all the things that being a battle brother would imply. Eldar Psykers can't buff Dark Eldar anymore, for example. I guess they didn't play test Allies too well and are realizing just how useful some of the stuff is.
"Fetch me another plaything. This one seems to have broken." -Urien Rakarth
Space Marine- "This planet is ours, witch."
Eldar- "No ... This planet is theirs ..."