Just to add my $.02...
Six Flags and Cedar Fair don't make sense to me...in that specific location. I think either could more than hold their own as a strong regional park for Florida residents, just in a different location (like, say, near US 27 or the north Orlando metro area, or even the Ocala/75 and Turnpike area). This would have been a perfect spot for Merlin to put Florida's LEGOLAND, as was Posner Park or Splendid China compared to where they decided to put it. Given their current state with LEGOLAND and lack of another current attraction concept that would compliment instead of hurt their existing business (mainly LEGOLAND), I would write them out of the picture as well. That leaves us with Herschend for the major amusement park players, and I think they're the one that would fit best into the area, but maybe not as a typical amusement/theme park development. I'm not quite sure what I would draw up as a development for Herschend in that location, but I don't think it would be a "normal" park where rides are the main attraction. I can see a well done dinner show by them giving Pirates some issues, or forcing them to up their game at least, and it would fit in very well as an individual component into the makeup of I-Drive and what consumers expect out of the area.
The idea of converting/retrofitting the existing structure into an indoor water park, at least in part, is a very interesting idea that I think could hold some merit, but I'm not sure that Schlitterbahn is up to that task at the moment. Given Great Wolf Lodge moving in off 535 I would bet that Kalahari Resorts is looking into the attractions area; and while I always envisioned them holding a location closer to WDW, perhaps the Artegon location would make just as much sense, and provide a little bit of a cushion from competing directly with GWL. Kalahari makes a lot of sense for the location, if you take a look at their resorts as a whole, as they're not just a hotel with an indoor water park attached. They also cover the convention and timeshare sectors as well, which seems like it would be a good fit for the area as an overall business.
In the end, I would lean more towards manufactured speculation to drive up prices, based on the "domestic with international ties/partners" verbiage.
However...what if that verbiage was reversed? What if this is an international player with domestic associations? My first thought with that is Wanda. I think they may have an itch to scratch by building in the Orlando market to compete with both US giants to prove a point after some of the barbs directed towards Disney by their CEO. This might be an opportunity that they could jump on, though I'm not sure it would necessarily be a "wise" opportunity.
Anyway, just my two cents on the issue.