I realize that it's difficult to write AI behaviour for actually designing fleets, but with a decent database of ship templates throughout the tech levels, it should be relatively simple to have the AI select the best one for the task at hand. I propose that if the AI encounters a player fleet (win or lose) it will start to bias its ship selection toward designs that have defences against the player's weapons and weapons that bypass the player's defences. Proper implementation involves the AI making sacrifical scouts (with minimal module tonnage) to probe player fleets, and the AI must remember which fleets it has already scouted (so it does not wasye time on a re-scout unless that fleet gets ships swapped in or out).

To my understanding the game already does this, how ever in a slightly different way. The AI cheats, and therefore simply builds ships that counter yours, after a couple of turns. However i could be mistaken.