Hey Steve,
Like the other poster, I can't see why a GA 12-er would have any difficulties or potential issues as compared to any of the other Taylor 12s. Pre-NT neck, they've stood up well; with NT you're golden!
FWIW, I've owned a 655 that I very much dug, and sold it only for my RT12, and in the interim had played a 3 and 8 series 12string. Every Taylor 12er (yes, from the 3 to the 6 to the 8 to my RT) has played superbly; better than any other 12-er I've ever played. Maybe it bears mentioning that I've loved/wanted a 12 string for decades, but never could bond with playing even the nice Guilds et. al. ; others sounded good, but never played good "enough" for me to want to take them home. Taylor's 12 changed that for me. And FWIW, years ago Leo Kottke returned to using a 12 because of Taylor's now-commonly-known slick action. All this to say, if you like the tone there's no reason to think that something will go awry with your Taylor 12, regardless of which series. And IMHO, with the NT you have a built-in longevity that other 12-string guits would kill for.
Edward