Most probably that's it. But I don't think it would be an easy task because it's a passive toggle. Especially that there was a request sometime ago like being able to customize which of your stats are displayed on the F9 panel, I don't remember what happened to it, but w/e, I think this is a bit similar to what he's trying to say.
It could be a dropdown or something in the F9 panel. I also agree with this for multiplayer matches, that the rank shown for players should correspond to the game mode being played.
Still, osu! is the primary game mode, so in unclear/unspecifiable circumstances, its ranks should be preferred.
You can already see your stats / rank at your profile, si maybe in a future, you will be able to see it in game.
Maybe when you click play / special / and choose Taiko or CTB, it will automatically change your stats in game, and it might even show at the f9 screen that you are in Taiko mode.
I don't know if this will be an easy task or even a good idea, but I do support it.