The Cacodemon hat looked like he had huge lips and he didn't have the tiny hair bits below him, comparing it to the sprites.
So how faithfull it was is why one could see the leak as fake, but then again, id games do a lot of throwback/fanservice stuff and it's not always accurate.
Even Smash makes mistakes with this.
Also, here's someone at id as Terry Bogard
https://twitter.com/idSoftware/status/1190353173652873228
Anyway, Doomguy's design could be his Eternal but even a bit closer to his classic look (Helmet painted grey) and maybe include Doom 64's antenna on his helmet.
For music, there's a lot you can do with Doom 1/2/Even TNT and Mick Gordon's work, while great, feels a bit limited and he has variety when you look at other games he made music for.
For stage, if there's a theme of dimension shifting, use it to represent different games:
* Doom 1: Classic Phobos/Knee Deep in The Dead mixed with classic Hell/Inferno, so it's technically Shores of Hell but we could get a variety of textures and maybe even FIREBLU in HD.
* 2: Similar but mostly focused on city/Earth and there may be a reference to Dead Simple, with Mancubi and Arachnotrons.
* Final: TNT and Plutonia combined like jungle textures and boxes with TNT written on it, may or may not include Archviles hiding somewhere.
* 64: The creepy UAC bases combined with the gothic, dark Hell and you can see D64 Cacos.
* 3: Empty looking labs with UAC posters and computers, maybe some corrupted screens where you can see Betruger or even a reference to the RPG games.
* 2016: Hell in 2016 with bits of Mars base/UAC and hints of UAC presence and something to do with Samuel Hayden.
* Eternal: Another Earth bit but different from Doom 2's part and combined with Night Sentinel/Heaven content.