It could go either way, but I think most planets will be era specific. Naboo and Kamino will most likely be Clone Wars specific, Hoth and whatever OT planets will probably be Galactic Civil Wars specific, and Takodana and Starkiller Base will be sequel trilogy specific. I could see Tatooine or Jakku mixing eras, however.
They might also be era locked based on tech issues. For the older games I can see how easy it would be to swap out the character models for certain planets, but will all the things going on with the new game, it might be harder to mix eras and planets.
Or I'm completely wrong and it's very simple to do. I'm not a game developer, I don't know how these things work.