Not really playing, but just played through the mod "Newer Super Mario Bros Wii" with a friend over dolphin netplay (pure hell but now we have PHDs in wii netplay which is way more convoluted than GC netplay which just works) which was a completely custom game made within the engine, and was really impressed, they did quite a bit that really made me dislike how nintendo has continued to treat their platformer mario series. With lackluster NEW titles.
https://newerteam.com/wii/Now what I really would die for would be a custom SMW rom hack balanced arround multiplayer.