I would like to see planets that are explorable, but aren't tied to the story. That way, if you are sick of doing Nar Shadda, Tatooine, Hoth, Quesh, etc. as you play alts, you can explore a new world instead. If you want to see the story, you will have to eventually go back and do the class quests. With these open worlds, though, you could level up in those and go back to the old worlds later to finish off the class quests. These worlds would have a story of their own, but they could also have a lot of freedom for exploration. I like quests and story, but I also like discovering new things.
As for planets I would like to see, Dathomir, Felucia, Kashyyyk, and Kamino come to mind.