Giby said in a Podcast with Gunsmith that XIII was developed with the console netcode in mind. But he also made the point that you can't just tack on GGPO to any game. The reason it works with so may games is because all those games are being emulated. (Blazblue uses something similar, but not identical.)
Although there's no official date yet, the game's most likely pretty far along. I'm sure SNK remembers the netcode complaints from XII, and I'm sure Atlus wouldn't be able to magically add GGPO to the game if people spam their message boards enough.
I think the only thing we can do is hope for the best re: netcode.
EDIT: The Atlus e-mail specifically mentions "vastly improved network functionality," providing "smoother, more stable online fights." They also mention "over half a dozen game modes to choose from."