it's not a 16 men raid per se.

U will split into 4 per team, in their own instances, doing your own investigation. I foresee that whatever u do, u will add up the investigation bar for that current session so the more people u do in that session/gathering hub, the faster u can complete the investigation hence the new elder dragon will appear and everyone like usual, do the quest in 4 per team in their own instances.

i maybe wrong though, we can only know after they show in their demo livestream tonight.

HR500 and self called noob lol.