Emulating software you purchased is not theft. Not sure how many times this has to be repeated. But OP’s point was not about theft. It was about whether or not retro emulation (of games no longer sold by Nintendo) would be a major priority for Nintendo’s lawyers. Either way, there’s nothing for them to go after here. Rom sites, yes; emulator software, no.
99.9% of people "emulating" software they apparently "purchased" are not using backup ROMS they actually created. They simply downloaded them from the internet