With the advent of Dataslates, Datasheets, and Datashits, models are becoming less and less exclusive to any given army. You can bring just about any combination of models you like nowadays (Tyranid players, my heart goes out to you). So it begs the question; would you cope with Desperate Ally status for a Dataslate or Datasheet? Obviously not for Cypher or Be'lakor, but for a Stormwing Formation? A Firebase Cadre? Any fairly independant option I can see being quite popular, despite Desperate Allies status.