Unfortunately, a walking path runs into similar issues as a walkway from GF has, you've got to cross a relatively wide boat channel, and a very active one in this case. It's also got to allow the passage of the MK stern wheeler for maintenance. Then the bridge has to accommodate wheelchairs etc so either very long ramps (as long as 500ft depending on required slope ratio) or elevators. Given the limited lad available (it can be seen on google maps) this is both very difficult and costly to do. Put it in the won't happen category.
As for the monorail, the expense as stated can be very high. But given the layout of the current track, the required turn ratios and available land the only two possible options are the Epcot bound track or the MK express track. The Epcot track is ok if you're going to Epcot but for what is likely the majority going to MK it would mean about 18minutes travel time to the TTC (6 minutes to EPCOT, wait in Epcot station, 6 minutes to the TTC) the switch trains to the express train and 5 minutes to MK. At the best you'd have a 25 minute trip. I think few people would want that over the boats.
The MK express line has its own cost issues and then the express stops being an express line once it was connected to WL. Three minutes out from the TTC you'd have a stop and wait. That then impacts all other trains on that line that have to wait for the train in front of them to clear that section of track. The line stops being an express line and defeats the purpose of being able to move large number of guests quickly between the TTC and MK at the busy open and closing hours. Not really a viable option.
