New Stones can be patched into the Carts, ala We are all playing Version 1.2 after the patch. But then why were Latios Megas in the game data at all? (Just in case? Or from an older version of the game before Online Patches were a feature?)
I Think the WHOLE POINT of the Mega-Blaziken Event was to tease us about Hoenn Remakes, and that All Starters will Mega-Evolve.
I think Classic Gen3 Pokemon are ripe for Megas: Absol, Aggron, Mawile, Oh Yeah...
The Must be adding Starters, and if they add those, then any number of new Mega can happen. More incentive to buy. (From GF's point of view.)