I did a quick look on the master unit list and found that they are not as exclusives as most people think:
Imp -HW Clan, IS Clan, Wolfs Dragoons
Shogun- Clan Blood Spirit, Clan Burrock, Clan Cloud Cobra, Clan Coyote, Clan Star Adder,
Free World League, Star League, Wolfs Dragoons
Annihilator HW Clan General, HW Clan General, Wolfs Dragoons, Kell Hounds, Lyran Commonwealth, Mercenary,
Republic of the Sphere
Hoplite Star League, Rim Worlds Republic, Capellan Confederation,Federated Suns, Magistracy of Canopus,
Wolfs Dragoons
You can throw out the Homeworlds. And the Imp C, frex the IS Clan list, afaik we have never actually seen it in a Clan force. Shogun? FWL, and I am wondering if that is a Clan Protectorate inclusion for the 3140s. Shoguns are also supposed to be rare as can be, IIRC almost extinct before the Dragoons got the Foxes to start building them again in Republic Era. Annihilator I already said was sold around some, but from most of it's IS time was mostly a Dragoon exclusive.
And just to satisfy curiousity, I looked it up for each design and checked the era boxes.
Royal Shogun/FWL- Early Succession Wars, aka SL units that went over, then goes extinct
Annihilator- Takes until the Clan Invasion era for it to go KH/Merc General . . . Early Republic it adds RAF & LCAF but note the original MAD II has 'Merc General' for Late SW- Renaissance when per canon outside of Barber's Marauders and maybe Kell Hounds the Dragoons did not let others buy the mech. So, Invasion era it was still probably restricted
Hoplite- All of those factions outside the Clans & Dragoons you mention ALSO, like the Shogun are Star League leftovers and extinct for those factions in the Succession Wars
So no, for most of the time since the Dragoons re-introduced those designs they were exclusive to them.
They've done art for the hoplite, so that one is extremely likely. Firefly would mean we need a good RecGuide firefly, as the 3060s firefly were yuck - single sinks.
Which is why I included the Annihilator and Hoplite in the prospective box, with the Shogun getting a Dark Age era variant or two I would like to see it. Gallowglas would also be nice as it gives us a heavy .