I know God has created worlds without number. I would imagine each world has a plan of salvation for them. But we all have our free agency. Would God allow a people from one world to visit another?
We have our free agency, but the space between planets is huge. The farthest mortals from earth have traveled is to the moon (I am hearing of plans to send people to Mars but I have no idea if that will happen). Thus it seems to me that for us to get people to other planets outside of the solar system it would require great leaps in our ability to engineer a spaceship that can do so, and an even greater leap in technology to do it in a time frame that is measured in less then generations.
So right now it seems that God is the only one that has the power to move people from one world to another. Which depending on how you define worlds could be exactly what He is doing every time He sends an angel to us here.