>>58804603All of the other Switch games have a Shiny Mythical available for completion of the entire Pokedex, and the two games with DLC require base game + DLC completion for that reward. That said, I don't expect for them to actually add the Home Dex completion rewards right when Z-A compatibility comes out (unless they do something like announce Gen 10 right afterwards). I'm expecting it later, probably a bit after Champions releases. And FWIW, the current "dex completion" rewards are:
>National Dex Up to Gen 7Original Color Magearna (Not shiny)
>Let's Go (Bulbasaur-Mewtwo)Shiny Meltan (the only way to get a Meltan with a LGPE origin mark)
>Sword and Shield (everything except Zarude)Shiny Keldeo
>Brilliant Diamond and Shining Pearl (Just the base Sinnoh Dex up to Palkia, the entire Gen 4 National dex isn't required)Shiny Manaphy (The only way to get BDSP Origin Mark Manaphy if you missed the event one)
>Legends Arceus (Everything in the dex, including Shaymin and Darkrai)Shiny Enamorous
>Scarlet and Violet (Everything in all three Pokedexes except for Iron Leaves, Walking Wake and Pecharunt)Shiny Meloetta
If they do end up doing one for Z-A it'll probably be Volcanion or Hoopa. Ingame though? Not really. There's Mable quests for doing it but you'll most likely have already reached level 50 before getting there even without grinding for it. Shocked they didn't do something like an Alpha Charm for completing the Hyperspace Pokedex.