The Throne of Glass series starts off as an amazing series with great storyline, creative world building, well written characters, etc. It is all you can ever wish for in a High Fantasy YA series. BUT, as the series went on, it also went downhill. The main protagonist has (had) too many love interests. Dorian in Book one. A little bit of Chaol in book one. Chaol in book two. Rowan in book four. We all know how TVD ended up with TWO love interests. Love triangles makes ship wars and honestly, no one likes it; so imagine more than 2 love interests. 

Romance aside, as I said before, ToG has great world building. It's gonna take a LOT of money to be able to bring it to life, or at least even something close, but if it is not handled by a huge network, the show won't do the series justice. And for the network's own good, I'm warning you that if you give the fans less than what's in the books, they're gonna get pretty mad. Fantasy IS HARD to adapt on TV.

Whitewashing. Pretty sure this is going to happen. It always does in TV shows and movies. The good thing about books is that you can imagine characters the way you want to (sometimes regardless of what they look on the books) which is why books should stay as books. 

If the show does happen and succeeds, the tendency is that it could impact and change how the rest of the ToG series progresses since the author hasn't finished writing all the book yet.. and we all know how succeptable she is to participating in fan service.

A Throne of Glass TV show would not do justice to the books for it would only focus on the romantic aspect of the story rather than the entire thing (since the producers probably can't afford to build the series' world) resulting to ugly internet ship wars. Basically, the show is just going to be another pathetic attempt on  a YA High Fantasy adaptation.