Reliable sources have said they look at it, and keep deciding not to. What WDW chose to do with putting all three lines on the same motor and choosing turning stations in Riviera and Boardwalk Inn parking lot closed off a lot of options to add on new lines. They didn't build for the future, making any new configuration that much more expensive to fix it.
The alternative is a bus or light rail running on their own roads not available to the public that may or may not be automated.
Currently, WDW seems content with the way things are buying more busses and creating more dedicated bus lanes and turning almost every traffic light into non-stop interchanges.