Makeb - New planet. Will be more story driven and based and rather than all out fighting it will involve some puzzles and more adventure play. It will not be released all at once but will be rolled out slowly.
New companion - HK-51. This will be available as a legacy item. You will need to be endgame and have some really high-level stuff in order to get him and it's also been said by bioware that you'll need a character on both sides in order to get him. Once unlocked he will be a legacy perk for all other chars.
New space combat. They will be re-inventing how space works in-game completely. They have said it will not simply be new missions but will completely change how they work. Besides this, they are being very tight-lipped on it.
Regarding the increased level cap:
Daniel Erickson wrote:I’ll say the short version is: even if you’re still leveling up, 50 is still the endgame. So you need to be able to play your character, and that’s where we’re focusing our leveling efforts
New species may be coming quickly after the Cathar and will be community-request driven.
New ops = next tier of operations. Nightmare is going to be made considerably harder as it is too easy at present.
Darth Hater interview: http://www.darthhater.com/articles/swto ... l-erickson