Hmmm, well the Imps have Interdictor Cruisers and also the ESSD is supposed to have them. Not sure about the Sovereign SSD class. They might havwe had them. If you ask me i think they're a bit too common in the game. I mean, look at the books, there aren't very many instances of Interdictors being used. I mean, the Emire didn't even use them in RotJ. Thrawn used them, because he was a master tactician. Maybe a limit on the number you can have, instead of having one with every single fleet?