Why would Disney bear any of the cost? How would Disney financially gain from it?
Are you positive the bridge could start at road level, given the narrow strip of land that exists and the height the bridge must achieve to allow boat clearance on a canal that changes depth? It is far more likely that there would need to be a series of ramps up to the actual crossing height of the bridge given that is a roughly 30' wide bank.
It would still need to have a gradual enough slope for a wheelchair or
ECV to access it, I doubt it could be considered a "required" walkway over an impediment for the purpose of ADA exemption, unless there were no other build options available. And I doubt the FL timeshare board would be too keen on using owners improvement money for a walkway that could not be easily accessed by handicapped owners of that resort. That would be expensive litigation waiting to happen. If you start at road level and figure an 8 foot rise over that 30 foot run of bank, you are looking at a very steep grade of 26.6%.
What "looks" like wetlands, and what is classified as wetlands by law are very different things. The treehouses don't look like wetlands, either. They don't flood regularly, but Disney had to design the new buildings to actually take up a smaller ground footprint than the original treehouses.