Considering that the Klingon faction wasn't really a faction at launch, and the Devs promise to rectify that, quite a bit.
You also have to consider the time and resource investment deploying a Romulan faction would take now too. They'd have to design each tier of ship, or just bump the starting point to level 2x like the Klingons, or even higher. There's also the contacts they'd have to develop, the main Hub environment, PvP hub environment. The Duty Officers, how the Romulans could get in on the FEs. How the Romulans could get in on the STFs. How systems would handle Romulans, how to balance them with the other factions, etc.
You'd also have to split the team down further, from the group doing the Klingon Content, the group doing FE content, and the group handling bug fixing/new stuff.
The could totally release a "Romulan" faction now. It'd be exactly like the Klingon faction was a launch though. No content missions, PvP and Killing fields as solely the means to level, maybe some explores. But there wouldn't be a whole lot to do, aside from leveling to cap then twiddling your thumbs until content comes out for the Romulans.