Diantha gave me the impression she was knowledgeable about Mega evolution, at least more so than Sycamore. We were never told how she got her Mega item either. Did she get it like the player? Is she related to the Guru like Korrina? Did she find it? I think that having her in these games will allow her to become fleshed out. Maybe she'll be a young adult or in her late teens.
I think that they could make the event longer than the Arceus and Lati events in HgSs. Maybe like the Celebi event in HgSs, except we'll be able to control the player.
Yeah that sounds highly possible I think you're right about Diantha being younger in ORAS.
It'd be cool if Steven and Diantha were related somehow or even partners..what with them both being knowledgeable about stones and having an interest in them, I think that might be possible.