Welp, as we celebrate OP's 20th Anniversary, we were in for a treat with some fanbase dividing news. The boys in Hollywood have allowed the executive producers of FOX's Prison Break (check that show out) to make a live action adaption of One Piece. [OP Fans Booing Intensifies!]
Now, looking back at live action versions of anime in the past, the track record is not that great. Dragon Ball Evolution and Avatar: The Last Airbender were big bombs at the box office and Rotten Tomatoes, Ghost In The Shell was mediocre despite all the whitewashing controversies, and fans are pissed off that L is black and Light is Disneyfied in Netflix's adaption of Death Note. So, let's go over the issues that OP could face:
Whitewashing has been a controversial practice in films for a while. Asian characters have not just been portrayed by white Americans, but have also been Americanized (i.e. name change to make it sound American). If Luffy, Zoro, etc. were portrayed by white people with bad hair coloring and makeup, the producers would be accused of being racist. The other alternative is having a diverse cast. However, fans would be upset to see an African American or female play a popular OP villain like Doflamingo or Buggy and then drama about SJWs would happen between fans of One Piece and the mainstream media. How would you feel if they actually casted a Brazilian to play Luffy, a Japanese man to play Zoro, and/or a French guy to play Sanji based on that one SBS about the SH's nationalities?
Of course, fans are gonna be worried about the CGI that Hollywood will try to make. In Dragon Ball Evolution, the CGI for the ki blasts were god awful. Now, you'll have to worry about how Hollywood will make Luffy's powers look good or bad on the screen. There's also the monsters of One Piece like the Sea Kings or other races such as the Giants and Long Arms. I'm more worried about the CGI than the casting at this moment.
Nothing can beat Oda's writing and storytelling, but Hollywood will take a stab at it and it won't end well. How will the story be paced? Will we start with Roger's execution and go to Luffy hanging out with Shanks? Or will we have other storylines to go through? Will Hollywood add some sort of OCs or depict another character as the main character? It could be a prequel-like story similar to FOX's Gotham.
Finally, we need to remember that these adaptations have not been popular amongst the American audience. 4Kids destroyed any momentum to make OP big in America, but the popularity has been rising back since the mid-00s, but I don't think it's enough to make the non-OP fan get into the series. I can see One Piece end up on one of the mainstream primetime channels like FOX or CBS, but it will probably air on Netflix (this could change if Death Note bombs on Netflix). We'll just have to wait for casting announcements and first trailers for now.