Silly by some people to believe this is any confirmation that the game's gonna be closer to Melee in gameplay just because half the players invited play Melee. This is just Nintendo trying to get the entirety of the Smash community together for a great Smash event, so they chose 4 players from each of Smash's two only relevant communities. It has nothing to do with the gameplay, in fact it is entirely possible that the people responsible for organizing the Invitational don't have access to the game either.
Odyssey is closer to 64 and BOTW is zelda 1.
A lot of their new games are looking back at what make them so great and taking them to in a new place.
This new game being based on Melee isn’t much of reach considering the trend.
Hardly a trend at all. Odyssey was based on the 64/Sunshine formula because it was very successful back then and fans really wanted it. BotW wasn't a throwback at all, it takes a lot of inspiration from Zelda 1 but it also takes a lot from the Zeldas that came after, and from loads of other open-world and also not open-world games. The end result is a game that's very much an entirely new thing when it comes to Zelda games.
Also, it's crazy to compare single-player and multiplayer games and pretend the same measures would be applied to both. The design focus of each one is vastly different, and with Nintendo's latest multiplayer game sequels (MK8D and Splatoon 2), we've seen them stick very closely to the Wii U formula. Also, Melee is, despite its large following, not the most successful Smash game nor is the second. Moreso, the two Smash games that were more successful than it were both its successors, and they used a similar design formula between themselves. I think it's far more likely that we see an evolution to the Brawl/Smash 4 formula than the Melee style being brought back, because it is more successful and it's also an approach that satisfies both Sakurai and Nintendo more.