|I did mean it as a campaign (hence "Has there ever been any consideration give to making a Mig variant", as all variants that I'm aware of are campaign researches).|
The SSD thing is a good point I hadn't considered, though how often is it that the Empire can't get a cloaking allied ship and do this anyway?
...as for the quote from Empire Strikes Back (lore nerd time): The Emperor's personal shuttle was believed/rumored to have a cloaking device, but normal troops/naval officers wouldn't be aware of it. The only in official canon cloaking device (other than that offhand mention) was of a ship in the Clone Wars CG show, basically a small transport about 90m long and very low profile (basically cigar/submarine shaped with a bank of engines on the back end), roughly 2x the length of the YT-1300 (Millennium Falcon), indicating that ships that small COULD have cloaking devices.
...but that cloaking device was also experimental and only used in that one occasion, meaning that such devices would have been pretty classified.
It's funny that that quote even exists, as we have no evidence in canon or expanded canon/legends that I'm aware of of any class of larger ship actually being fielded with cloaking devices (a CR90 Correllian Corvette/Blockade Runner was fitted with an experimental one in the final campaign of TIE Fighter the game, but it was unstable at hyperspeed and exploded, and that campaign arc/mission was concurrent with the Battle of Endor, with the final debriefing talking about how we were awaiting word of the Emperor's most-certain success and glorious triumph over the Rebellion...)
So the quote itself is kind of funny if you think about it.
It should be noted that the cloaked prototype transport was from the Galactic Republic, before the Emperor reorganized it into the Empire, meaning the Rebels might have known about or had access to it, but neither seems to have fielded it in the war.
As for the Defiant - that's technically a borrowed Romulan cloak. Not only that...I'm not sure the Diplomacy class REALLY fits the Defiant. Sure, a cloaking Diplomacy would be awesome, but if I was to give the Feds a cloaking ship, I'd do it with the Vendetta. FAR more balanced due to the more fragile (and easily capturable) Vendetta...and that the Lizards already have a cloaking variant, meaning in VGAP lore, it being part of the "technology exchange" between the Feds and Lizards (Feds give Lizards Loki and a handful of ship designs, Lizards gave Feds...what, nothing back..?) would actually make a lot of sense (Feds give Lizards Loki - ability to detect cloaks - and Lizards give Feds a crappy cloak on a weak hull? That sounds at least a little more reasonable.)