Disclaimer -- I have not been on the test server and am going on other people's comments.  Basically, it sounds like the IJN SS5 is in general worse than the SS4 and the only thing you get is TBs (I'm guessing only a couple). and you have to be on the surface to launch the TBs.  This stinks.

I am not at all interested in this ship -- I already get beat too often by KM SS4s and a couple TBs will not make the situation better.
   This would be REALLY interesting -- much better than TBs.  The only way I could see TBs being worthwhile is if the sub could launch at least six at a time and be able to hold at least 12 at the beginning of the game.  This would be sufficient firepower to keep the sub behind your line where you could surface without risking BB bombardment. 

Got one idea -- don't make it torpedo bombers launched from the IJN SS5 -- make them mini subs!  We could operate them just like planes and they could hold one torpedo, just like in WW2 (well the japs often held two torps, so give them two airborne torpedos that are launched at the same time)

The differences from planes -- 1) mother sub does not have to surface to launch  2) can't be seen without sonar 3) mini subs have limited sonar range 4) limited speed  5) can be destroyed only be torps or dc or hh -- no aa.

Still have the mini-subs able to return to the ship for reload, like a plane.  And give it limited "flight time"  This would mimic the air cycle of the sub.  If it runs out of air, it dies (like the plane running out of fuel).  Don't give the mini sub the option to surface -- it has to stay underwater the whole time it is deployed. 

This would be REALLY interesting.  Help the gigantic mother sub against other subs, but would still limit the difference it would make.