Alsakan - Core World that once tried to usurp Coruscant's place as capital of the republic. Perhaps a storyline based upon a new Alaskan conflict and an attempt to become the new capital or defect to the empire with promises of social importance and power.
Bothawui - Home of the Bothan Species one of the most successfull spy net works in the galaxy and turning point in the conflict between the empire and republic prior to the treaty of Coruscan with the sacrifice of Jedi Master Belth Allusis . Shadowy war and imperial infiltrators bent on erasing the morale boost given by this event could make a great storyline.
Gamorr - Home of the Gamorreans a well known race of slow witted and brutal mercenaries that always seem to be exploited by all sides in a conflict. Perfect world riff with storylines to prevent or aid the empire from using these brutal aliens or perhaps preventing the hutts from using them to take on both of the main factions.
Hapes - Capital of the Hapan Empire, it was about this time in the time line that the Jedi wiped out the Lorell Raiders a group of pirates that used Hapes as its base of operations to terrorize the galaxy. Reformation and unification under the Queen Mothers come at this time and perhaps. a story about that or the destruction of the Pirates with aid from both sides of the Galactic conflict.
Iridonia - Home of the Zabrak and the site of dozens of battles between the mando and republic as well as the Republic and Sith during many wars including the jedi civil war and it could easily be central to the new sith war as it has sympathies to the sith through the ages and to the republic and is a major strategic point on the hyper lanes.
Kashyyyk - Do I really need to explain why ?
Lehon - AKA Rakata Prime Capital planet of the Infinite Empire and a planet in ruins prime potential for search for advanced technology and a race to recover weapons of the Rakatan in an effort to get a head in the world , maybe a hub world like Illum for the next story arc.
Malachor V - Destroyed and heavy in the darkside and a huge wound in the Force this place could be an interesting place set up kind of like the Fleets where instead of going from place to place upon a whole planet you could hope around large chunks of the newly formed asteroid bett, a heavily darkside themed story line about Darth Traya and her academy and the death of Malachor V would be kind of cool.
Malanose - Malanose was a world within the Gree Enclave, on the Outer Rim of the galaxy, which served as the primary world containing the Crafter and Researcher castes of the Gree civilization. Much like Lehon it could serve as a place where the rush to recover lost tech is placed at the forefront of the storylines.
Mandalore - This could be the first real offensive the republic put up the invasion of the Mando homeworld to destroy the mercenary support of the Sith Empire.
Obroa-skai - The reputation that had developed over the centuries was that the complete knowledge of the galaxy had been gathered within the computers of Obroa-skai's information repositories. This could be done much like Coruscant but perhaps entirely indoors with the great libraries being the focal points of the story and planet.
Dxun - Rather then use Onderon itself Dxun could be used as a high level daily hub but with a twist missions are only given out to those that have darkside 4+ giving you a reason to be darkside and a set of quest and gear to reward you for getting that high of a darkside score.
Ossus - Similar to my idea for Dxun this would be a high level daily quest hub for light siders with quest and rewards for those with light side 4+ set in the ruins of the great libraries and rediscovering ancient jedi secrets and weapons.
Thyferra - Primary Bacta production planet in the galaxy it can easily be seen why this would be a hotly contested planet revolving around the need to secure the Bacta for your side, maybe a flash point or operation about it.
Umbara - Umbara, informally known as the Shadow World, was a shadowy planet within the reaches of the Ghost Nebula. It was home to the Umbarans, a race of pale near-Humans. A planet forever enshrowded in darkness home of many spies and assasins.
Ziost - The original Sith Homeworld this would be a cool world to explore and rediscover in service of the Imperial Reclamation Service.