There was a time when I would give Jim Hill the benefit of the doubt, or at least tolerate his writing style because the content was at least amusing. That time passed long ago, and his credibility has been shot for a long time. Other readers have pointed to the likely reasons he wrote this article, so there's no point going there.
Everything else Disney is doing--from X-Pass (including multiple coming NextGen queues along with 'memory-targeted' product development, among data mining and other things) to the currently announced expansion totally flies in the face of this rumor. These are huge CapEx projects inconsistent with the impetus behind a fifth gate that, more importantly, won't be done until around 2017. So between 2017 and 2021 Disney will start building a fifth gate? Right...
This doesn't even take into account economics and guest habits that have gradually been changing over the past several years making the idea of a fifth gate even less viable. There's no sign that these habits are going to reverse themselves anytime soon.
So unless Jim Hill can now accurately predict the future of the economy AND vacationing habits on top of moves by Disney, he doesn't currently *know* that this is going to happen.