OP, you should title your suggestion a little more clearly. I thought this was a suggestion to propose the M17 Whizbang as a modification for all Shermans that used it in-game, but after I read it, it sounded like you are proposing it as a specific vehicle with it.
T40/M17 Whizbang was the launcher design and the name designated for this launcher, NOT the tank design nor the name of the vehicle equipped with the launcher; I want to clear up any misunderstandings here. If added in-game, it would be named just “Whizbang” or “M4 Sherman Whizbang,” or whatever. Just like the Sherman equipped with the T34 Calliope is named “Calliope” in-game.
Furthermore, do you have any credible sources on the launchers found to be mounted on the M4A3, M4A4, and M4A6, let alone Shermans armed with 76mm guns? I am very skeptical of this claim. Were you just throwing Sherman variants around without in-depth research?