I think it was "sorta" okay for the Klingons to get a Kar'fi since it was one of their own unique enemies and it's completely unlikely we'll see those guys as a playable faction.
But a Breen ship...there is still a remote chance we'll get sme kind of reborn Dominion faction and I don't think we should "waste" ships for such factions this way.
It's a phenomenon I observed in games like "Navy Field" and "World of Tanks" where playable sides were added some time after the game went online (in case of Navy Filed half a decade later) and the result are unit lists that are completely chaotic.
In World of Tanks the Russians have a British Premium Tank and when the British become available they'll have a different version of the same tank as a normal tank.
In Navy Field it's the same with the Germans who have an Italian Premium Battleship, the Americans having a Russian ship and the British having a French one.
The Russians and French are there and it's really weird to have the Dunkerque and her sister ships the Strasbourgh in different navies (and with different stats even though they were identical).
So I'm sorry, but I'll have to say no to this proposal of yours.
And I'd rather like to see a Gorn Battlecarrier with Kar'fi based stats and a reversal of the Tactical and Engineering BO and console slots instead.
With your proposal we'd also be running the risk of such a ship falling into Federation hands resulting in a continuaton of the JH fighter weirdness.