Technically, it's already $16! People buying it have to pay almost $1 in taxes upon purchase - not something Disney tends to mention! I do disagree with Grasshopper201, though. A form of G+ will be with us for awhile. There will be tweaks, but it'll be with us. It lasted for years at DL with a very similar product, MaxPass.
But those people who predicted a few years ago FP+ would not last - turns out they were right! So who knows!