I personally think that this might be an original theme. Merlin's major thrill rollercoasters don't normally tend to have IPs (aside from the obvious example of Saw), as they are marketable enough on their own. A hyper coaster, depending on scale, would almost definitely be marketable with an original theme.
However, if they did want to go for an IP, then I reckon one of those drama series on Netflix would be right up Thorpe's street. I can imagine
Orange is the New Black: The Ride or
Riverdale: The Ride going down a storm at a place like Thorpe. I've never watched any of these, so I can't really comment on how they would translate into a large outdoor rollercoaster, but as the park went with TWD, it wouldn't surprise me if they went with this sort of IP.
Or maybe... they could go with
Stranger Things: The Ride. It's a highly popular Netflix series, AND the title would imply that the show even lends itself to Merlin's favourite sort of theme... the sort where strange things are discovered "during recent excavations"!
I've never actually watched Stranger Things, mind, so I could be talking a load of utter garbage!
The only Netflix IP I have watched that I would like in a theme park is Lemony Snicket's A Series of Unfortunate Events. The show is great and the books are all fantastic, too! But I think this would be better as a dark ride or enclosed coaster. Also, it strikes me as more of an IP that Alton or Chessington would go for than one that Thorpe would go for, if you get what I mean.
But I reckon Project 2020 will be an original theme, because a massive roller coaster doesn't exactly need an IP to market it, does it? I hope that Thorpe takes inspiration from the level of theming of Wicker Man and applies it to this coaster, whatever it is. Anyway, I reckon that whatever Project 2020 is, it will be a huge hit for Thorpe. Merlin now have a good idea of what works at Thorpe and what doesn't, so they will be refining this attraction to make sure that Thorpe's target market love it.
P.S. Sorry for the long post.