The official Marvel YouTube page started a live stream called "ANNOUNCEMENT"

So far it featured a guy going up to the camera and placing near it a chair labeled “Chris Hemsworth” (Thor)

The whole lineup:

• “Chris Hemsworth” (Thor)
• “Vanessa Kirby” (Invisible Woman)
• “Anthony Mackie” (Captain America)
• “Sebastian Stan” (The Winter Soldier)
• “Letitia Wright” (Black Panther)
• “Paul Rudd” (Ant-Man)
• “Wyatt Russell” (US Agent)
• “Tenoch Huerta Mejia” (Namor)
• “Ebon Moss-Bachrach” (The Thing)
• “Simu Liu” (Shang Chi)
• “Florence Pugh” (Black Widow)
• “Kelsey Grammer” (Beast)
• “Lewis Pullman” (Sentry)
• “Danny Ramirez” (Falcon)
• “Joseph Quinn” (The Human Torch)
• “David Harbour” (Red Guardian)
• “Winston Duke” (M'Baku)
• “Hannah John-Kamen” (Ghost)
• “Tom Hiddleston” (Loki)
• “Patrick Stewart” (Professor X)
• “Ian McKellen” (Magneto)
• “Alan Cumming” (Nightcrawler)
• “Rebecca Romijn” (Mystique)
• “James Marsden” (Cyclops)
• “Channing Tatum” (Gambit)
• “Pedro Pascal” (Mr. Fantastic)
• “Robert Downey Jr.” (Dr. Doom)

Surely this must be for Doomsday. The directors chairs at least imply it's film-related and not an announcement for a comics event.

I know this can't be everyone - neither Strange nor Wong are here, nor are any of the Hulks?