Humm. My understanding is that only the non voice companions are accessible in the expansion. When you wake up 5 years in the future, you have none except for that Beniko space herpies sith. As you go through the chapters you can get new ones that they have been showcasing like Darth Marr from the Revan expansion. As for your old companions, the once with voice actors like Vette are gone. The non-voice companions like Broonmark you can reunite with, but your choices during the quests will determine if they rejoin you.

It's been kind of weird with the information they have released. They said that once you start the expansion, you can't go back. But that dev-tracker link says that you can. I hope you can go back and are not locked into some new central hub zone. It will be a deathstroke to the game if they separate the non-subs from the subs like this. I can't find it now, but I specifically remember reading that the free level 60 is expansion only because you haven't done any of the story-line quests and you will be preset full dark or full light depending on the class.

It may have been one of the E3 or developer videos where they said all that...