Outer Rim's FUCKED. They can't add new planets without making the two-lane board even longer, and it's already too fucking long. They can't add new contacts without adding new planets (there are exactly enough planets to have all contacts in play every game). And adding new planets that are supposed to REPLACE existing planets (randomly or otherwise) means breaking delivery missions, bounty missions, jobs, EVERYTHING.
You can add more cards to the market decks, that's literally all you can do without overhauling the design. There's room to add new characters (though not much, because most of the ones who aren't already playable are already in the game as contacts, so you can't use, for example, Dengar -- who is on the fucking cover for some reason), new ships, new jobs, new cargo, new bounties (about half the contacts don't have bounties, you could do them), new encounter cards for each planet -- just deck inflation, basically, that's all you've got. And that doesn't fix any of the game's core problems.
Outer Rim doesn't need an expansion, it needs a time traveler to cancel it before it was announced.