However, a Romulan faction would make more sense in having nothing to do with New Romulus except for what the Captains decide to do. [...]
I don't understand that notion. New Romulus is, in my opinion, perfect for a STO Romulan faction. They will be allied with both other factions, so participating in, say, Task Force Omega to fight the Borg, in events like the 2800 arc, even fights against the True Way, just make a lot of sense.
By contrast, a Romulan faction that follows Sela, the Tal Shiar, and the Iconians, could not possibly participate in all that.
Of course, there is a third Romulan faction in their current civil war... maybe they could walk a middle ground... but personally, I would be happy with a playing Romulan starship commander who follows D'Tans leadership... it would just work best within the overall STO story.