Just a few things we don’t know off the top of my head:
What neighbors are returning from past games besides who we’ve seen,
what role does Harvey serve? Are the multiple islands for play with other players?
How do holidays work? We haven’t seen a single one referenced.
Where exactly are places like museum, able sisters, etc. we haven’t heard or seen anything on these locations despite their owners being in the game.
How big is the island exactly, what are the build limits, resident limits, and other limits?. It looks bigger then new leaf but we don’t know it’s full scale.
What’s Isabelle doing? We see her in a nook uniform but what is her job, what is our job/position in town? Are we the mayor or di we just get given this responsibility.
And arguably the biggest, how do amiibo work? All those villagers had cards and we could get special Nintendo neighbors. Are any of these characters returning, are there new Nintendo neighbors?
These would all be great things to know in some form before release