I'd go for this. It would be nice to be able to have a semi-random fight with the Breen outside of the current repeatable missions we've all played countless times. It would make them feel more like a "real" enemy faction.
We don't "need" one, this is true. But those who are at VA who do a lot of exploration and defera missions might appreciate something to mix up the drudgery of routine.
There is only so many times I can look at the green stars of B'Tran cluster before I get ill.
Plus, as already mentioned, the Breen would be the main antagonists of this cluster. Yes, you can already fight the Breen any time you want, but only in the exact same missions we've already played. At least star cluster missions are somewhat randomized and you dont know for sure what type of mission you will get.