They're pumping them out at roughly 3-4 weeks which is way to quick in my opinion, stunts the growth of worlds with newer ones opening so soon it means players just hop from world to world. I'd recommend helping a current world grow, the rim ca be juicy for growth.
It is not always 3-4 weeks. It can be anything from 2 weeks to 2 months. It depends on business needs and availability of the markets, but there is a trend.
As it stands right now, there is no news concerning a new world. Generally, a new world starts after one closes. I am not sure if we are close to closing another world just yet, but it is something I will look further into though.