I believe it will happen sooner than we might think.
#believe
I'd honestly rather skip Third and go to Zero/Ao, then return to Third. Third scares me because of its text heavy star doors and dungeon crawling nature. It's a game I definitely want to play, but one that I don't feel has a very strong appeal for the casual fan. Maybe I'm being pessimistic, but it would almost undoubtedly be the worst selling game in the series, I think. If Third tanked and ruined Crossbell's chances of coming over, that'd be it. Zero, on the other hand, is a much more cohesive JRPG that would get much better reviews from the typical player, and would push an Ao localization closer to reality if anything.
Third is like the bonus chapter I want if everything else goes well. When the franchise hinges on success, and a weird game like Third comes along, it makes me nervous to think about it releasing before the Crossbell duology.