And I doubt that Nintendo could make an emulator as efficient as the Xbox 360 emulator on Xbox One. They aren't that good at making emulators tbh, there are more accurate emulators out there than their Virtual Console games.
This is something people often ignore. The 360 emulator on the XBO is probably the most efficient emulator there is. It is helped by Microsoft being primarily a software company, that has developed computer Operating Systems and other PC software since their inception. Sure, Nintendo is a software company in the sense that their games are software, but neither Nintendo nor Sony (nor basically any other company on the globe) has the same expertise as Microsoft has in this field.