I hope the Remans stay on their new world and leave the rest of the galaxy alone. They are half of the two worst things about Romulans in the recent movies (the other half is the new look--tattoos and spiky ships).
The Romulans from TNG/DS9 were perfect, thank you very much.
I am sure they will make an appearance, but I'll probably be choosing Romulan or something else.
Hirogen are...wannabe-Predators. (God, the last few years of Star Trek came up with some pretty stolen/copied concepts!) They will probably be attached to one faction or another. If the Dominion faction makes it in game, probably them, but the bets are on Romulans being the next faction and...probably Cardassia after that.
For any Hirogen fans, that means quite a long wait.
I really hope that Cryptic have a good plan for introducing any new races into the game. I can't think of many games that have 4 factions cause your making it harder for players to find groups for PvP and raids. And both Romulan and Cardassian have the added problem of not being in at launch so either be appealing enough to draw players away from their established characters or attract new players to STO. As such I really hope its sooner rather than later that we see them as after a 6 month or a year people that are still playing will be fairly established in fleets and not want to return to noob status. At least not as a main character.