For most of us, the Omega Ruby and Alpha Sapphire demos don't drop until October 21 — and, even then, it will only be available to folks who are a part of the Pokémon Trainer's Club. But you don't have to wait to see what the demo holds, if you don't want to.
I'm especially curious about Buzznav on the bottom of the screen — it seems like you'll have news with you all the time. That feels surprisingly modern, given how we all walk around with phones and such now.
In any case, even if you watch through all of this, you'll probably still want to play the demo, as it comes with some special goodies you'll be able to transfer over to the main game. Like mega stones!