Official, at first ones a month, if proven popular, on weekly bases, Market and Tournament day.
Market will attract PvE players, Tournament PvPers. If it's on the same day we will have a chance to mingle together.
I know, it is a sand-box, players should decide it all themselves However, it would be so much easier to know that, let say every Wednesday or Thursday there is an Event in Capital.
Maybe it will change when the game is in full swing, but at the moment walking the streets of Capital is a very lonely experience.