Hmm. I would prefer a full faction, but realise that might be too much in one go. What I would suggest is this (my idea of a mini-faction):
1) At the opening screen, add a tab next to the fed/Klingon character creator tabs entitled "Other". This would open to the "other" factions, as described under #2. The tab would be openable for any unrestricted slots a player may have.
2) Create a list of mini-faction races, with a color scheme with the name of the minifaction behind it. Starting with the Romulans, as an example, you would list the Romulan races on a green background with the word Romulan centered on the line semi-transparent. When adding other minifactions, you would use a different color scheme with the faction name transparent, etc. More races could be added as desired/necessary.
3) The starting Romulan races probably should be Romulan, Reman, Hirogen and Romulan Alien. Although this would take quite some resources, Cryptic is well known for its customizable character creator and would be well worth it. In time more customization choices could be added to the Romulan Alien as has been done with both the Federation and Klingon Alien. As a new minifaction is introduced, starting with at least three races would be adviseable, but do not introduce a race until there is a good amount of customizations available. As an example, if adding the Dominion faction, I would suggest Jem H'adar, Breen, Dominion Alien, and Vorta.
4) Give the minifaction a unique social hub. Although time consuming, each minifaction should have its own version of ESD or First City. This hub would have mail, bank, stores, everything necessary for a character/player. Do not allow the minifactions to go to fed or Klingon only places (again like ESD). This will be both a sort of unspoken promise for number 5, detailed below, and to show that just because we can now play this faction, it still is a seperate entity from the Klingons and Federation.
5) Start the new minifactions at level 40, with three unique introductory missions and work in access to older missions. Over time, add new missions and eventually expand the level ranges of the minifactions. Personally, I would like to see each even numbered season add more to the klingons and minifactions, but understand that might not be possible. Starting
at higher levels would allow the slow addition of new resources for the new factions and make it possible for them to some day be fully fleshed out.
6) Add a few new pvp maps with each minifaction, allowing for new ways to pvp. Allow the minifactions to sign up for either fed or klingon side in current pvp matches to allow those matches to get started sooner. New pvp maps could be setup specifically for the minifactions in various ways. An example, when adding a second minifaction, say the Dominion, a pvp map could be set up so Klingon, Fed, and Romulan could sign up for one side, but the other side could Dominion only. Other possible matchup combos could be Rom/klingon vs fed/dom.
Just my random thoughts/desires. Note: I used the Dominion as my example a) because they are probalby my third choice for a new faction; and b) because I can only see the borg as level 50 PVP opponents (my sensibilities say borg character not for me )
A bit of an odd comment, why would you remove content from any game? The patrols I did on my main character, I liked them, they were fun and a decent XP source but nothing else. Most of them weren't too repetitive either.
Adding more patrols to the KDF (not the excess we see in Fed mind you) is an acceptable way to provide moderate quality cheap content. Repeating this for future mini-factions would lessen the cost of introduction.
I like the idea of sub-factions on sides, split alliances, etc. Adding any race is resource intensive but that is a good way to do it given the wide range of content in the game.
One thing I never seem to hear or be brought up is the never ending stream of bugs being brought into the game. There are zones like Defera you are literally playing around bugs that never get fixed, episodes broken and bugged for ages, and so many issues from the S6 introduction still un-resolved its a crime. Why is there no priority on this? Player retention = money, nothing drives players away faster than endless bugs.
Serious work needs to be done on QA for STO, and pushing serious known bugs through to live should be forbidden. Most MMOs will patch test then hold the patch until those issues are resolved; you can't test for 2 days, ignore feedback and push to live, you will lose players steadily.
Actually what I'd like to see is, in my opinion a little easier than say a new feature episode or playable faction. What I'd like to see added is maybe more customizable options for players bridges, like the option of having damaged decks or even some customizable decor options for the Captain's Quarters like a generic list of items you can place in preset areas i.e. trophies, plants, photos, maybe a retro-tv like Lt. Paris had in ST: Voyager.
It is time to seriously start working on lowering the klingons starting lvl, until people can start a Klink from lvl 1 the kdf will never be on par with the feds, no matter how many ships you throw at us.
Sure, there are more fed-people out there, but that is exactly why this needs to happen. If it is too much work just let people start a lvl 20 kdf char from the get go, I am sure there are good ways of covering the gap up with some background story involving a rite of ascension or something like it.
As long as it is required to have a fed char, of course numbers will be on the fed side.