I would absolutely try the new game, but I would judge it based on it's own merits and not just as "the new 14." If it's a good game then I'd definitely stick with it at least until 14 starts to notably wind down.
Honestly, though, even if the new game wasn't great I'd probably still slip away from 14 regardless. I enjoy it now but give it a couple more years (or more) and the diminishing support/content it would inherently get with a new FF MMO on the block, I doubt there'd be enough to keep me sticking around.
