This isn't a live action adaptation of One Piece per se. Instead, it's a live action collaboration with Monkey D. Luffy.
Picture: Comic Natalie
Comic Natalie reports that actor Hiroshi Abe stars in the upcoming television special as a yakuza member who ends up in the hospital, where his characters mistakenly eats the gum-gum fruit that made Luffy all rubbery. Below, you can see a photo of Abe's character in the hospital after he's eaten the fruit. So, it's One Piece made real, but in a slightly different way from what you'd expect. I guess.
According to Sanspo, Luffy shows up at the hospital, and while the live-action rubber limbs are CG, Luffy will be animated as seen in the above promotional material. (Note: that website Natalie says Luffy is CG.)
The veteran actor is quoted as saying, "Since this is the first time I've appeared with Luffy from One Piece, I wasn't really sure what to expect, but since this was unlike anything I'd experienced before, I had a lot of fun doing it. I'm eager to see how everything comes together with the animation."
Considering how most straight up anime adaptations turn out fairly rotten, this sort of "anime collaboration" might be a smarter choice, right? Right? Eh, let's see how this one turns out.