Currently, the Breen series of episodes is at the very end of the leveling up process. It seems that it makes sense to move this up to right between the end of the Romulan series and the Cardassian series.
The Breen series gives us some very cool ship equipment (engines, shields, deflectors). You can outfit your ship, but then you move directly to the Borg series, which gives you even better ship equipment. This is immediately followed by hitting level 50, where you can get the MAKO set. This means that your Breen equipment lasts about 3-4 missions before being totally obsolete. That seems like a waste to me, and all the rewards are just bunched up together.
Why not move the Breen series up? This would mean getting fitted with the Breen equipment around level 39-40. At that point in the game, the extra powers would be much appreciated by players. By the time it starts to grow obsolete in 8-9 levels, you're reaching the Borg episodes, which is a perfect segueway for upgrading.