Well, what's this? It seems as though Doom, Doom II, and Doom 3 aren't the only classic Doom games in the pipeline. We might be getting a throwback from the 64-bit era.
PEGI, the European ratings board, has a new listing for Doom 64. It was first noticed by Gematsu, but the entry has since been deleted. PEGI's rating only covers PC and PS4, but any new release would most certainly come to Switch and Xbox One too; that's exactly how it worked with Doom and Doom II.
As far as leaks go, ratings boards have one of the better success rates. But, if not part of the QuakeCon trio of surprise Doom releases, when might Doom 64 launch? Possibly as a pre-order incentive alongside Doom Eternal this November? Doom is always hiding so many secrets.