And that's what's holding back popularity. Not "uncompleteness", but Cryptic's unwillingness to simply allow people to dive in.
That's purely wishful thinking, the KDF (and any hypothetical Romulan factions) will never be as popular as the Federation. This is not a bad thing, nor does it reflect poorly on the other less popular factions. Its just a result of the way Star Trek is.
That said, I'm baffled but at the same time relieved they haven't added more ships to the KDF.
Baffled because it can't be that difficult, heck,they could sell slightly cheaper new ships using the pre-existing ship costumes with new layouts and people would accept it since its established in canon that the KDF tends to keep the external look of their ships constant.
Relieved because adding more ships would really bring parity to the factions (an extra 20 low levels would be more of a hindrance, ask any fed player...). If the factions were equal I'm 100% sure all the little bribes to play KDF (mostly based around Dil and EC) would be taken away rather than added the blue side. Since my KDF alts have become hard working farmers in this post S6 and S7 world I'd hate to loose my easy Dil! There was once a time my KDF tac would stomp all over the Borg in her Vo'Quv or Guramba.... those days are just gone. The grinds mean I can only really have one main supported by several farmers .
But...OP, do not feel bad about people clamoring for a Romulan faction and prophetising the end of the KDF. There is just no way that Cryptic can release anything as good as what they are fooling themselves into believing is being released. Even with all the added developers (a good chunk of whom are probably over a NWO in a mad dash to get that released) Cryptic has a history of under delivering.