Wizards will add a category on their Discord server after the announcements. Seems like something big that people can start talking immediately. Maybe "tarrasque-sized" as a 5.5 preview UA will be released at the end of stream, with feedback on Discord channel (do you remember the recent tweet from Crawford, about seeing something about new rules real soon?). Or a new Videogame (as games, tabletop or video, will have each a category).
Or... A beta of their VTT. That would be tarrasque sized change indeed.