I for one would like to play a Romulan and if they do a Borg faction that would be the most awesomeness ever. And I know it would take too much work and there very busy but it doesn't have to be. If they simply make the faction and a few ships for it. For example Romulan Tier 1: Some little ship, Tier 2: Bird of Prey, Tier 3: Mogai Escort, Tier 4: Deridex Cruiser, And Tier 5: an IRW.
And for missions they just need one defend your sector, one explore mission, and the rest will be custom made by the players in the foundry.
They can make it ignore it when there working on something else and add a little bit at a time when they do have time. It can work I think
Please don't flame me if this can't possibly work just say its impossible and I'll simply wait for when they decide to add it.
A lot of players have commented on the forums that they would love to expand STO with a Romulan faction. Unfortunatly with limited resources the time frame for this has been said to be toward the end of next year. Your idea of creating the basic framework to get it going, and then tac on content over time, was already done with the Klingon faction to much critisism .