>>27488016Here's a flaw with this picture. Previously, there hasn't been a Mega Stone slot, in the sense that there only exists one "Mega Stone" for the trainer, and it's been built into the bracelet. Yeah, it's removable, as shown in Origins, but it's odd that the trainer's Mega Stone wouldn't just be in the bracelet already.
One explanation is that the trainer's Mega Stone is relegated to postgame content. But seeing as Pokemon Mega Stones cannot be traded, why not just relegate all Mega Stones to postgame content? If Mega Evolution is postgame only, I doubt they would be handing you out Ampharosite and what not before you're introduced to Mega Stones.
They did essentially do that in ORAS, though. I could see this going either way. There isn't conclusive evidence for either side.