I think both the Feds and the Imperials could do with a medium ship that competes with the newer Alliance stuff for a similar hardpoints / speed / agility capability.
Assuming the plan is more of the “MkII” approach …
A FAS MkII that brings the modules / hardpoint loadout from the Gunship to the flight model of the FAS (or at least moves in that direction) given this really should be fundamentally possible.
A Clipper MkII that shrinks a little to fit on a medium pad and adds an undernose C2 or C3 hardpoint in return for losing a little internal space.
That would give both superpowers a viable competitor to the Chieftain, Fer de Lance and even Krait MkII for that matter.
For the fourth ship? I’d selfishly like to see a Corvette MkII that trades a little shield / hull capability for decent speed (like Cutter level or close to) as a warship that slow just doesn’t make sense to me but that seems unlikely as it would kinda be an unfair buff to the Feds with the Imperials not getting an equivalent.
Cobra MkV? I could see FDev wanting to do that as the “classic” Elite ship and it being the 40th (?) anniversary year. Not sure what it could bring without just becoming a defacto replacement for the current Cobra, though, which is arguably already “best in class” for a small ship.