Demo savedata probably won't contain any Pokemon info (aside from, maybe, Greninja, but they can just easily put the flag and generate all the data on-the-fly or in the main game). But it's worth trying to extract pkm data from the RAM of running demo, that is indeed possible. Although PK7 format can differ from PK6 in size at least, I doubt they changed the core algorithms of pkm generation/block shuffling/etc. (if they did, good for them). So... I'm almost sure that is possible for pkm files at least.
Aaaand... there's a high chance of press-release leaking. That should boost the process immensely.