This has been wished for multiple times in the past. Last time it was brought up, I did give this idea some thought. While this might sound like a good idea on the surface, there are multiple problems that arise when you stop and really think about how the submarine work, it's capabilities in term of speed, firepower and endurance, especially submerged capabilities vs it's target.
First, let's look at the fleet submarine(USN sub) capabilities. We'll take as our 'average' mid/late war 'typical' fleet boat, a Balao class USN fleet submarine. It had a 21 knots surfaced flank speed, with optimal range of 11 000 miles@10knots. It managed a whooping 8.75 knots submerged at flank bell. Let's note here that under the current setup, our carrier group sail at a permanent flank speed of 35 knots, meaning that if one of these spotted a cv group from a trailing position, there is no way for it to get into position. Even if you are ahead of the group, that is no guarantee that you'll catch it. Of course there is always the possibility of spawning one close to a port when a CV get close but then there is still the problem of getting in attack position as in that situation, you'd be submerged and limited to 9 knots vs the 35+ of the CG. Also note that the submerged flank bell endurance is quite limited. And once your batteries start to deplete, it cripple your submerged speed by that much. A type XXI U-boat enjoy a much improved submerged speed at 18kts. Yet still not enough to be practical against one of our CG.
We also have to consider the problems brought up by the ASUW aspect. The introduction of the submarine will create a need for specialized weapons to handle the threat. Some we already have in bombs that could be used against surfaced or very shallow subs, some we don't as the depth charge and some ASUW capable ship like the corvette/destroyer, the PBY (and other sea recon planes). Then we have all the aspect of acoustic detection to consider, as much for the sub as for the destroyer with ASDIC, passive sonar suit, active sonar suit for subs, radar(that were used extensively during mid-late war by the US fleet in the pacific). Capabilities and vehicles and systems that would have to be introduced at the same time as the subs.
One last thing to consider is the time scale at which AH is played. It's basically real time so for a fleet boat doing flank bell @ 20-21kts surfaced(Type XXI U-boat did not go faster submerged or sufaced), we're looking at 1:15h to cross a 25 miles sector. The point is all sub-sim games I played(sub command/dangerous waters/silent hunter 2-3-4) have a time compression capability, allowing the player to skip the tedious part and jump right into the action.
I'm not saying it can not/should not be done. I just have a hard time figuring how this could be made realistic enough, up to AH standard, and yet fun. It would be hard to make it so without profound changes to the way surface warfare is done. We'd need many players manned boat sailing all over the place to make it worthwhile to up a sub. Just chasing CV group would hardly justify the introduction of subs by itself as, as of now, our CG woulkd easily outrun most, if not all, subs used during WW2 and they are just too far in between. If some sort of resupply convoy system could be implemented along with the subs to provide some targets, it would be another thing.
My 2 cents on the matter.
