I'm really excited for this. I never imagined seeing One Piece back on TV; let alone uncut on Adult Swim. I always said it would never happen. [AS] re-branding their Saturday night anime-block as the revived Toonami is the best thing that's happened to CN in years. Without it One Piece probably never would have seen the light of day. Now we have a medium that can air the big three uncut in a big way.
Honestly, I don't think noobs to One Piece are FUNimation and Adult Swim's priority. They're doing this for the fans who have been begging for OP to get back on TV for years. If they aired weekly from the beginning it would take some four years to reach where they are now, which by then would be another four years behind both the dub and the sub. And that's presuming the show survives on TV that long. The old episodes have been on DVD for a while now anyway and plenty of them are available for free on the site–not to mention the whole series is subbed online and simulcast.
Starting at Water 7 is the best thing for them to do now. It's not far behind the DVDs and the arc has never been aired on TV before. Skypeia (though unfinished) was on TV five years ago. Skipping ahead to the beginning of the next arc just makes the most sense.
And even though the audience will be mostly One Piece fans, I do think this can be a new beginning for One Piece as we know it. Now we have the uncut FUNimation dub televised on Adult Swim with Bleach and Naruto. Not only do they get to air One Piece on TV again–but they get to totally re-brand it too. People who tune in to watch Bleach, Naruto, Eureka Seven, FullMetal, etc. will now see One Piece as a legitimate anime on par with other mature Shonen titles. The 4K!Ds product has been off the air for so long now that the show's prior image can be erased. Even though they're starting so late in the series, an uncut Water 7/Enies Lobby story can draw in a lot of new fans--who will then watch the earlier episodes if they feel so inclined.
One Piece is an incredibly long show. For the relatively small fan base it has in the States, we're lucky FUNi hasn't dropped it yet. And they will need to not only hold on to the franchise, but also keep dubbing it for at least ten more years or so if we can ever hope to see a complete dubbed product. God knows where the anime industry will be by then, let alone Toonami, Adult Swim, etc. One Piece's success on the air waves will be HUGE in going forward with the franchise. Unfortunately, right now the path forward just can't comprise going back to airing episodes that were already seen on TV (albeit by 4K!Ds) nearly ten years ago. But if there's a show that can pick up new fans 200 episodes in, it's One Piece. Each arc presents a new independent storyline and builds on every character. You don't have to know what happened two hundred episodes ago to get behind what's going on now.
Also, it would be a good idea if Toonami eventually aired movie 8 on TV. Those long-story-arcs-crammed-into-one-movie films can do a good job of bringing new fans up to speed.