You do realize all the Nintendo online games like Smash, Splatoon 2, Mario Kart 8 are all peer-to-peer right? The only thing associated with dedicate servers is matchmaking but once synced up, the only thing between the 2+ players are their internet connection itself.
To respond to a question OP stated, I would actually be against a Melee rendition of being added through NSOs. I can sense the additional input lag from a mile away and why would I play Melee on terrible only when Melee on Dolphin is not only free but also has rollback netcode? I know I'm in the minority when it comes to this aspect in particular but I would not be in support of a re-issue of Melee if the online isn't as good as Slippi's rollback.