Good? Bad? That opinion seems to vary from person to person, and that's part of why Billy's afraid of it.
For some it means creation. Others suggest the opposite.
The Demiurge mythos connecting to Billy was established in Kieron Gillen and Jamie Mckelvie's Young Avengers run "Style>Substance".
Whilst dimension hopping, the Young Avengers came across a planet inhabited by little cuties who gave the first name drop.
Later in that run, America Chavez identified Billy as the Demiurge, her world's creator and her personal hero whom she would cosplay at a child, during a flashback montage at the celebratory dance party held when the young heroes defeated the big bad.
Al Ewing has been largely instrumental since, in continuing the Demiurge mythos and Billy's ties to the title, in various titles including his New Avengers run, where Billy was part of Roberto Dacosta's team (also the run where Teddy receives his sword and establishes the Knights Infinite). Billy's been identified as the Demiurge by other magical entities and characters like Dormamu and Doctor Doom, further cementing his destined role.
There was also a Doom specific story (I believe it was online exclusive?) where Doom mentions the Demiurge, and I have screen shots on my phone of the panels, but I don't know what the actual book / issue / story was. Anyone know?
The screenshot I took is Doom addressing Stark and he says: "The day is coming soon Stark. The day everything changes. The day of the Demiurge"
He goes on in another panel explaining: "Afterwards, magic was changed. The basic precepts altered. The unwritten rules I had spent a lifetime studying... re-written. My magic was gone."
The pics I took were back in June 2018.
I'm 90% certain it has to be an Al Ewing thing.