If One Piece were to come back to Toonami (and now that Naruto has returned, my faith in that has risen greatly) they would have to start with the first episode. If they started somewhere in the middle like others have suggested, and someone said this as well, the Toonami viewers who haven't been exposed to One Piece simply wouldn't care. No one can jump into a show mid-way and expect to be able to understand anything less than the characters' names. It would be like if Toonami acquired the rights to Naruto Shippuden, and then just started with episode 245. Neon Alley understands this, that's why they air 4 episodes each week leading up to their eventual weekly premieres, but then again they have the freedom to do so (they have the freedom to do that with One Piece though, too ).
One might argue that it will take ages to reach Water Seven, or Alabasta, or any of your other favorite arcs. The Naruto Vs. Sasuke fight is pretty much the Water Seven of Naruto, and that's going to take some time to reach going by one episode a week.
But I'm just looking forward to watching Naruto on TV again. I'd feel the same way with One Piece. And hey, whether its Naruto or One Piece, if they want to watch the latest episodes or catch themselves up faster they can just buy the DVD's.
(Or watch episodes on FUNimation.com and Crunchyroll if they don't want to pay very much and don't mind subtitles)
–- Update From New Post Merge ---
Speaking of which the Season 4 episodes on onepieceofficial.com are getting to the good stuff!