RN level 120 DP gunners were said to have rocket launchers LOOOOONG ago.
However AA rockets were glitchy as heck and got removed... and i'm quite sure SDE won't experiment with those anytime soon.

most allied nations were well in front of weapong develeopment, so giving it to high tier ijn ships
would mean giving it to med lvl allied crew?

NF plays around 40-to late 42 i'd say, there's plenty of "modern" equipment that was in the war, but not in the game,
most of it because it would ruin the game (if HH are mortar-like go figure what rockets would do ingame)

there is a matter of balance and keeping the game "pure". there is a reason why some BB projects are around but not jet aircraft projects, let alone homing torps, rockets, missles, etc.

...sonar decoy, hamburg sprouting V2s, USN harbor launching a nuke.

Yup sounds fun.

forget the harbor, Iowa was eventually fitted with nuke shells