I think a lot of your questions are just a wait and see type of thing.

The data centers are simply meant to place players of a region on a server which their peak times coincide and their language is the same.

It just seems like people think just because the data center is close they will magically have wonderful pings and no lag response, which they can get from any data center any where in the world. The reason lag was bad in version 1.0 wasn't because the data center was in Japan, it was because they had a really bad data structure and poor infrastructure.

Don't feel like you have to choose a server based on your region or you will have a really bad laggy time. You won't notice the difference in lag between a server in your region or across the world. If you want to play early mornings (NA) then pick a JP server because their peak time is early morning for us. If you want to play a lot during the day time (NA) then pick the EU server because their peak time is noon for NA. If you want to play at night when the NA peak time is, then play on a NA server. That's really the only advantage besides language to having regional data centers, the lag we are talking about 100ms maybe 150 at worst, which for a mmo is absolutely nothing.

I can't speak Japanese and my best time to play is NA peak time, therefore I shall choose a NA data center to play with English speaking players that prefer to play after 5pm CST or so. While I love most of the JP players I've encountered, I'm quite tired of JP ONLY groups or groups that can't use voice chat because no one speaks the same language...