Dusk Golem
A 21st Century Rockefeller
The series has never actually dropped a narrative unless it was something explicitly never mentioned. They could afford to drop the G-Virus sub-plot because nothing ever explicitly came of it, and they could change the nature and name of the Clay Virus because it was never fully discussed outside of Japanese guidebooks.
Alex is mentioned both in BH5 itself (as "Alex W.") and its Lost In Nightmares DLC. He is also mentioned in Archives II. I'd wait until Takenaka takes the writing helm again before he is ever mentioned again, though.
I guess a better way to word it would be to say that they leave things hanging. There's the ever popular 'what happened to character X' questions (though to be fair, this game did go deeper into the gates of characters long unexplained, namely Sherry and Claire), or the questions of certain plot points that haven't been explained properly in years with a few more arising every once in a while (what or who is the third organization being an example of an older long-running mystery, or smaller variables now like who was Jake's mother?).
There's also characters who live that I never understood why they let them live or plot points that seem like they could lead to something but then they never do. Such examples would be like why Nicholai lives in Resident Evil 3, why does Wesker make an ambiguous remark for Steve when leaving (
Actually, the C-Virus uses the T-Veronica Virus as a foundation, doesn't it? And isn't Steve the last remaining sample of the T-Veronica Virus?
The regenerating monsters in this game... Are they ever explained? They are definitely really similar to the Ooze, and I don't know if what they are is ever explained in this game.