The only instance of Smash compositing together different unrelated retro series/games into a single piece of content I'd have no issues with is if Dream Land GB turned out to be a composite stage like was teased - and that's solely because Smash was and still is awfully low on Game Boy content. It's why I don't like the idea of 9-Volt in Smash, why sneak in Virtual Boy rep through another series when you could just add a Teleroboxer fighter or let the VB walk with it's lanky legs? Why relegate Nintendo's pre-gaming toys to just "WarioWare weirdness" when you could put in a president or miniature marsupial to treat the whole library with respect?