How about Corusant ONLY IF it is an actual city/planet rather than a 10 things to do Taris like in KI. I'd like to see bounty hunter missions, bounty hunters for hire as followers (some very powerful but expensive). How about custom return here to get paid from different organizations like the Exchange, Cerka, etc. for doing custom quests? A rogue Jedi here or there to either contend with or based on your alliance purchase their loyality as followers. Custom shops with a wide variety of items. How about a senate house you can visit to listen to debates on your events in the galaxy.
Assignment of day/night settings to vary player effects/powers/combat etc based on their stats. (It's NEVER night in Star Wars Land)
An actual house or home base other than the Ebon Hawk for storage and the like. Ability to leave followers for as long as you like "at home" without any ramifications.
I agree Alderaan should be a given as it's a CORE planet as core as you get with the galaxy revolving around the people it produces or the planet itself.
Sleheyron is another Tattoonie knockoff that they won't do just because of that; global appeal.
Private worlds like Rhelg would appeal to a few but general SW fans would be like "where the heck is that?"
I think if the plot keeps with what it "hints" at, it will be a Sith Empire from outside the known rim where the Sith Lords escaped too when the original Sith planet was overthrown or the like.
I really think they should rehash ALL of the worlds encountered in KOTOR 1 & 2 plus add at least 6 more for the new core content of the game. Unique ones like Jediphile and others mentioned like Alderaan and the like.
Stretch off to custom oddball planets with vague references or the like and your in trouble. Thats why in the end they'll only go for core worlds that are very well known like Mon Calimari that are fundamental to the SW universe. Or thats my 2 cents anywho.