And you’re not going to get it because 1) the characters are not deep or unique enough to carry a film by themselves, 2) the lore isn’t popular enough for the general audience to justify centering films around it, 3) Universal—as a creative entity—is going to prioritize the marketing/advertising potential of the HHN name and tie that to parks.
You say the fandom is getting bigger how are you actually defining “the fandom.” Are you referring to how many folks ask about the lore on Reddit/Discord? If that’s your measure, it actually isn’t that more active than it’s been for twenty years. Or are you referring to the total number of people attending the event? That number IS increasing, but it’s not lore and original characters driving that increase. It’s IPs.
Universal recognizes that producing a wide-release film focused on Pennywise Jack, Harley Quinn Chance, Pumpkinhead Pumpkin Lord, Mary Shaw the Storyteller, Phantom of the Opera Usher or any other icon will immediately get dismissed as an imitation. That’s because those characters ARE imitations. Their individual lores are also fairly shallow and contrived as well. The only thing that actually makes them compelling at all is the fact they’re taking over a theme park. If a film removes the theme park aspect, then everything about the icon becomes hollow.