... what would it be? Noldor discard, Silvan pop in and out of play, Dunedain reap benefits from keeping enemies engaged, etc. What flavor would you give to Beornings if this trait were developed?
To an extent, the developers seem to look at the existing card pool, then find a way to emphasize existing strengths when developing a trait. For Dunedain they've given a it of love to Signals, and they developed the whole archetype around engaging enemies, which already existed with the Son or Arnor from the core set. There was also precedent for the Noldor discard mechanic (the two tactics allies and all Erestor). Developing a trait around these existing functions breathes life into old cards.
Right now we have a Beorn hero and ally, and the Beorning Beekeeper. One does direct damage, one does a big combat round then disappears from play, and the other is a beast but is immune to player card effects. Pretty disparate set of effects, other than being combat-oriented... wonder how we could tie them all together?