Gonna bring up Smash Brothers again. That random element is a major annoyance, which is why some of us are really worried about the quests in Dominion. We hate game elements that mean one side can get a sudden advantage for no reason other than luck of the draw.
Would suck if the enemy team was all grouped up to take one of our bases, we decide to let it go and push a different lane, and suddenly a quest comes up that rewards them for taking that base.
Would also suck if an objective came up that was on the other side of the map from where most of our team was while the entire enemy team just happened to be in that area.
On the other hand, if the quests are triggered by particular events in the game, that would make them more fair, but it would also make them predictable by experienced players. It would mean experienced players could smell a quest coming up and get into position early, giving them an added advantage over newbies who will be wondering why the quests always seem to favour the other team. If they always trigger for losing teams, you might get people intentionally holding back so they can trigger quests, like people slowing down so they can kill the race leader and steal 1st place right before the finish line in Mario Kart.
Either they are random or they are predictable. Pick your poison.
Sorry if I sound antagonistic. I'm not trying to **** over the great work Riot does, but you guys have to know that these are some of the fears we have from our past bad experiences with other games. If you do figure out a quest system that is fun and yet isn't random enough to unbalance games, that would be great of course. I hope that when Dominion arrives, you'll have all these issues ironed out nicely.