Honestly, we don't know yet. It is a stand alone expansion, so you won't need any prior version of the game, but we don't know if trinity will be included with it. It will have all the content from trinity (that they don't change in Rebellion of course), but you may not be able to play with your friend who only has Diplomacy for example. Likewise we don't know if it will be available for retail, it depends on how economically viable/possible they think it will be.
