Torp XP was severely nerfed across the board about the time GB2 was introduced.
They removed earned XP and replaced it with shared XP. So now Kita, TB and Subs get no bonus for doing attacks.
In a Kita you can single handedly kill a BB6 (yes some of them ARE that dumb) but still only get the same as killing 1 DD.
As for TB, well that was THE reason to go TB in CV. Now it is the same XP in virtually every game, win at one level, loose at another, game after game. Yes fighter shoot down helps but most CV players get the same average shoot down per game.
But with all the shouting about SS, it was the EASY way out to limit subs, limiting them to shared XP as well, where they should have balanced them by making sinking a sub profitable.
So it is unlikely that XP will change because the Sub haters will bleat on about a buff to over powered subs even if something is done to keep them in check whilst also not increasing their effectiveness.