This is purely speculation, but...
If it turns out that Inkay and Malimar are octopi, I’ve got a possible theory as to why Inkay’s evolution involves turning the 3DS.
This hinges on the fact that traditional octopus fishing in Asia usually involves leaving some kind of earthenware pot or container in the water, and later hauling it up to reveal an octopus inside. Maybe Inkay’s design includes a container, and to get it to evolve you have to turn it upside-down so it falls out?
If it turns out that Inkay and Malimar are octopi, I’ve got a possible theory as to why Inkay’s evolution involves turning the 3DS.
This hinges on the fact that traditional octopus fishing in Asia usually involves leaving some kind of earthenware pot or container in the water, and later hauling it up to reveal an octopus inside. Maybe Inkay’s design includes a container, and to get it to evolve you have to turn it upside-down so it falls out?