(Not to be confused with the WvW buff)
There don’t seem to be many (afaik) traits/abilities that factor in whether your group is outnumbered or not, but I think such a mechanic could be a useful fit in the game, particularly in WvW for certain professions.
Two examples to illustrate my point
Warrior’s grandmaster trait Defy Pain (Triggers an invuln at 25% health), what if in addition to that it triggered a +1s stealth on the Warrior per enemy outnumbering allies in a 600 radius?
Warrior’s Sure Footed trait increases stance duration 25%, what if it added a +1s duration on the Warrior per enemy outnumbering allies in a 600 radius?
etc.
Also something interesting to potentially factor into the earn-able/unlockable end-game traits coming later this year, IMO.