https://www.theverge.com/2017/11/16/16649934/amazon-studios-fantasy-genre-tv-adaptation

TV networks should look to other fantasy novel series if they want to find the next Game of Thrones.

HBO CEO: We didn’t want a Lord of the Rings TV series because we already have a Game of Thrones franchise (http://variety.com/2017/tv/news/hbo-lord-of-the-rings-show-game-of-thrones-1202627131/)
“I’d rather own our IP (intellectual property) 100%… and I’d rather have the ability to work with a product that is inextricably linked to our brand,” Richard Plepler said of all the Game of Thrones prequels in the works. Plepler also pointed out that HBO’s sister company, Time Warner, will profit from the Lord of the Rings TV series since it’s being co-produced by WB’s New Line Cinema division.

The Shannara Chronicles is a current series based on a fantasy book franchise, granted its entire budget is probably equal to GOT's catering costs.

Not sure why we need another Lord Of The Rings adaption, there's plenty of other fantasy franchises that have yet to be adapted, though I doubt we'll ever see one based on Stephen R Donaldson's Thomas Covenant books, given the hero is a leper.

And it does look like Sony has bought the rights to Robert Jordan's Wheel Of Time series: 14 books, each book at least 800 pages long, plenty there to draw from.

There was also the shortlived Legend Of The Seeker, based on Terry Goodkind's Sword Of Truth books, but it wasn't very good.

If done right Robert Silverberg's Majipoor Chronicles and Michael Moorcock's Elric series could make for good television.

I was looking forward to Stephen King's The Dark Tower movies/TV series, when it was still in the hands of Ron Howard, but then we got the horrendous film last summer, which tried to stuff multiple books into 90 minutes, and that was just one of many problems with the film.