Well, I’d say yes they should make a Legend of Korra movie, not only would it make the fans happy, but it’s also a financially sound plan, I mean, despite all the bad reviews the last film did fairly well, and the fan base has only gotten bigger. However, I’m not of the opinion that Book 1 should be remade into a movie, what’s done is done. Instead I think a movie should cover an entirely new story arc, perhaps even new characters. A film adaptation of the series has so much potential to add to the established lore of the universe, create new stories, show new parts of the four kingdoms.
That being said, TLK is much more streamlined than ATLA was, there aren’t any episodes that don’t add to the main story arc, precious few side plots, and it comes to a definite end after only one book. Clearly if one WERE to make a movie of this series, and I’m not suggesting they should, then Book 1 would be fairly easy to convert to such, without too much controversy around cutting out parts and whatnot.
I still can’t see how a movie could possibly be better than the show though, which is why I think they should make a unique movie, perhaps they could do a prequel, Aang and Toph taking down Yacone, or jump ahead and look at the next avatar after Korra, or even one of the past avatars, maybe Kuruk fighting Koh. There’s just so much potential, and so many stories left untold, that there’s no need to go over material covered by the show.