Do we already know what happens with this item in SM?

Literally nothing.

Hell you can buy them in a store for 3000poke a piece

It's just as the name says.

An npc gives you one and says it represents the tapus.

I wouldn't be surprised if this was the true Tapu leader, kind of like Regigigas. Hopefully his ability is some sort of Slow Start Terrain.

>>29851192
It's the true head of the Tapus' Z-Move.