Vistas in combat
People viewing vistas get the Invulnerability buff (so you can actually watch the cutscene without worrying about a stray mob murdering you), allowing vista usage in combat would – and I’m not even using hyperbole here – completely destroy WvW. Zergs would just camp vistas in EBG keeps (also vistas right next to BL garrisons) and fire up a script to spam F to become permanently invulnerable until defenders leave in disgust, leaving them free to take the keep.
They could just change it so that you are no longer invulnerable when viewing vistas. Who would take a minute to ignore everything and look out over a glorious landscape when there’s 4 angry trolls clawing at your face?
Since ever?
Most of the vistas are in open areas where people rarely just camp for hours on end.
Every class besides necro has enough tricks to make it to them without entering combat.