Something to keep in mind is that earlier in 2015 (May I believe); Universal Creative had a "Mass Hire" for any position within that. And to add, this plot had concepts back in the early days of IOA being operational. The situation should be possibly by that they are reusing similar concepts from the Vivendi/GE days but implementing it on a larger scale with different IPs.
As
@JungleSkip mentioned; this could be in the manner of the third gate being much like how Tokyo Disneysea is handled, where it has a general original concept but uses IPs to appease both audiences.
In essence, if they started planning in Late 2014 and started infrastructure work in December 2016/January 2017; they can start vertical construction probably in January 2018 and then having it ready by Late-Summer/Early Fall of 2020. At least as a guess, Infrastructure work could take about a year at most, for the company of Comcast at least. But in the end, its just my guess and I can probably be wrong.