Since it's been mentioned that Season 7 will be mostly story based, I think we might see the big secret being the reveal that the Federation has actually been under Undine influence for years - meaning the Klingons have actually been right all along!
Vice Admiral Laurence Corrin - USS Trafalgar
Captain Takaram ch'Rihan - USS Khellian
Captain Korax joH'a' vo'poH - USS Hartnell
General Hothkar, Son of Ta'lon - IKS oDwI'