Whatever happened to this concept anyway? The whole idea of gem shards being used to posses things.

We see it here, there was that one gem powering the spinning-room temple and the one gem that possessed the lighthouse. Not sure if Lapis counts, as the mirror was more a means of interrogation.

Kinda seems like they had a couple ideas from early in the show's life that they didn't know what to do with.

Guess that concept pretty much dropped due to outer space hijinks becoming more prominent