I feel like at this point all smash needs is BOTW themed stage and a Mario Odyssey one. The great plateau would work extremely nice, maybe as that other zelda skyward sword stage! As for Mario odyssey I don't know what they would do, there are a ton of landmarks they could take advantage off but I think the most known one is New Donk City.
At the end of the day we still don't know anything and we can only speculate! Let's sit tight and wait for E3!
RE: How I would Reboot Super Smash Bros. Part 4: Mario & Zelda Stages