There's an existing tunnel under the waterway for World Drive. It even has a sidewalk. The sidewalk ends around where the monorail crosses. Once there, there are no roads to cross to get to the T&TC. Google maps says they'd need about 1000' (2/10 of a mile) of sidewalk to complete the path.
But, getting to the side of the road that has the sidewalk is a bit of a challenge. The shortest path would require an additional traffic light or pedestrian bridge on World Drive in order to have the shortest paving (200'). Because the ground is sloped down to form the underpass, Disney could build up the land on either side with a gentle incline and thus have a "ground level" cross over World Drive near the water bridge (noting that this would require extensive bank grading and reinforcement). The cheapest path without a light or bridge would be to bring a path off the back of the bus area, since that requires only paving 800' of sidewalk to connect to the existing sidewalk. Unfortunately, for those at the Contemporary, it would add about 1/2 a mile of walking over the shortest alternative.
The total distance on the short path is about 3/4 of a mile, and a bit over a mile for the long (cheap) path.
To complete a trip to Wilderness Lodge, you'd need a traffic light or bridge on World Drive and a 300' section of sidewalk to connect to the end of the sidewalk going to the cabins.
Of course, in addition to the sidewalks, traffic lights and/or pedestrian bridge, the sidewalk will need lighting.
It's all doable, but Disney needs to see a reason to do it. I wonder how they internally justified the VGF path to MK?