Well I guess I'm in the minorty here but I kinda don't want the 688(i) to go away. Bye Bye any cold war scenerios. (rember Bill's fantasic Red Storm Rising campgain- there was no Va class boats or even Seawolfs in RSR!)
As for replacing one of the Kilos
!! All three classes of Kilo are very diffrent boats.
Maybe tack on the Va class to the 688(i) roster? and have a switcher util to change between pure 688(i) interface and the Hybrid SW-688(i) interface? Heck if anything replace the Seawolf.