That's right, it's not like that. Nintendo sues when they know they can win, as in the Yuzu debacle where keys were extracted and distributed in order for the emulator to work. There's nothing like that necessary for NES, SNES, or even (as far as I know) N64 or Wii. So no, Nintendo would not sue.
Dolphin ships with a bunch of keys in the source code[0]. So do almost every other emulators for any console from 6/7th gen consoles (ps3, xbox360, gamecube), see delroth's post on the matter here[1]. It's really not that simple - jurisdiction matters a lot, and also Nintendo's own priorities.
Nintendo will not need to sue because they know that the only way Apple will ever allow a NES, SNES, or N64 emulator is if Nintendo publishes it themselves and offers their own games for it through IAPs.
There is more money in having Nintendo be happy to support iPhone platform with games than having them feel insulted over a low revenue app that is also on the platform.
