A new world will open when a old world is full. These are the guidelines:
Speed 1: 45.000
Speed 1,5: 37.000
Speed 2: 30.000
Speed 2,5: 25.000
Speed 3: 20.000
Speed 4: 17.500
But remember, these are guidlines. Sometimes a world will open while the world before was speed 1 and only have 42.000.
This world has 35.000 players, so just w8 a few weeks
I hope I've giving enough information. This information is from the dutch server, but these are the same (I could be wrong with that).