I'm stunned how little integration there is between the Switch and Miitomo. "Win this outfit and decorate your room, which only people playing the app can see."
Agreed. There's this weird half-integration where you can use them for avatars but it doesn't seem to let you even import your Miitomo/ID Mii, etc.
Not to mention that Splatoon 2 wants you to assign a Mii to any new Amiibo even though the above is true. I didn't even end up scanning the new Squid one I got (mostly for its looks rather than the bonus though) because I was too lazy to figure out the Mii stuff then and never got around to it after.