My response to both bolded sentences is a strong "Meh."
On the first one, like someone else said earlier in the thread, a prime piece of real estate like that won't go untouched if a developer really wants it, whether it's already built on or not. Also, I think there are a lot of developers and operators that would love to have a project like this, but don't have the cash and/or stones to build it first. If Skyplex goes under, I think there will be multiple groups lined up to take over. It's theoretically (you'll understand why I say theoretically when I mention the traffic below) a great location, and outside of the roller coaster, probably a perfectly sound concept. Let's be honest, if it weren't for the roller coaster this thing would be largely uninteresting as yet another mega retail center and no one would think twice about it. Given that, I hope they're designing the structure in such a way that if it goes under and other developers don't want to deal with coaster it (i.e. the track and any externally visible supports) can be removed with relatively little pain.
As to the second, it already is a massive traffic nightmare and I'm not sure how much worse this could possibly make it. Between about noon and 10pm/midnight (depending on the season) Sand Lake westbound fluctuates between being backed up halfway to Universal Blvd. to backing up past the merge point for the Kirkman ramp. Eastbound isn't as bad, but it will sometimes back up to or beyond I-4 if there's enough traffic wanting to turn north on I-Drive at that intersection. I-Drive itself is a mess north and southbound at that intersection as well. I've been in a backup beyond Universal Blvd. on southbound I-Drive a few times (in the middle of the day, to boot!), and have seen northbound traffic backed up nearly to the Kings plaza. The proposed overhead pedestrian walkway should help the light cycles and traffic flow significantly (20 seconds off each light cycle for pedestrian only crossing time and pauses in traffic flow yielding to pedestrians add up really fast), along with more parking garages being built to help spread out traffic and encourage walking between points of interest. If they can eliminate most/all at grade pedestrian crossings, that alone will improve traffic flow greatly. The only remaining impediment to traffic flow becomes the I-Ride Trolley.
They really screwed up in planning I-Drive initially by not creating sufficient set back requirements to allow for widening, and also in not actively trying to direct some traffic for things like Pointe Orlando to Universal Blvd.