along the years manny companys made nes,snes and gba emulators and released their games running on them and nintendo could never do anything, its no ilegal to make an emulator to run your games, thats why is nvidea hired the dolphin dev and now they have their own gc and wii emulators all they need to do is pay for rights to put the games on sale on their digital shop.
square enix not wanting to make a ds emulator is very understanding, emulators are long works and expensive and some wont even work depending on the console,like ds and 3ds manny games rely on alot of touch screen forced stuff and dual screen use wich wouldnt work at all on ps4/xb1, even on switch the dual screen worldnt work too well because the switch cant be stationary virticaly unless you make your own custom stand.