I'm going to do a little speculating here about the Confederation and Kilrathi use of the older ships.
It seemed like Confed's tactics changed during the war with the Nephilim, to more battleship style broadside strikes, instead of fighters escorting bombers in to launch their torpedoes. Or at least a mixture of both of those tactics. From Star*Soldier alone, it seems like there was a lot more capital ship to capital ship battles in the Nephilim War, than there was with the Kilrathi War.
So, going along with the topic of would the Confederation and Kilrathi have used older ships in the war with the Nephilim and the tactics change....would they have refitted older and heavier capital ships (Iowa class battlecruiser, Concordia class supercruiser, Gettysburg Class cruiser) to meet their need for ships capable of a heavy broadside attack, or waited until a new class had been designed?
It probably wouldn't be off for Confed to have made some mobile-starbase type ships. The Midway was hailed as having many support facilities, allowing it to operate with access to fewer central assets. The Vesuvius was still in service and apparently more were built. Then there was the Armada Lexington, essentially a carrier converted into an armed forge ship.
With the wormholes and no standing knowledge of the enemy's territory, Confed could have built the equivalent of fully self-sufficient warships which would have been as large as a Behemoth or Hvar'kann. Those ships could then act as expiditionary forces or the center of attack fleets until bases could be established and proper logistics set up.
Yeah, I definitely could see more uses of these larger ships for mobile command bases. An there use for going into uncharted territory. There firepower definitely would've been useful in tight situations. I would say that the Confederation wouldn't even bother with building brand new bases, when they already have these monster ships around acting as a base. They probably would only add on to them to meet the additional additional needs as bases. Look at the Port Broughton, she was converted into a base (Though Star*Soldier's description of her paints a picture of it being in serious disrepair).
Also, I would love to see what a finished Behemoth would've looked like. I'm sure it would've been extremely formidable, if it's defensive systems and any additional offensive weaponry was finished.