Subs, supply convoys, and ASW ops for DDs are all on my list of things I'd like to see. I've also got a couple other suggestions:
1. Add a main battery gun director player position to the CA, where the player can operate a rangefinder to nme ships, shore guns, buildings, whatever. Players in the 8" turrets see a highlight of some sort on the target the director player is ranging. Also, the range from the director player shows up on screen for the gunner players, so they adjust their elevation to match it.
2. Add 2 2ndary battery gun directors for the 5" guns on the CA and 1 on the CV. This would work as above except it would only help 5" gunners, and could be used on planes as well as ships, PTs, and shore objects.