Here is a great link that details a huge problem WDW has with ordering new monorails:
http://www.monorails.org/tMspages/TPBeams.html
Look at the beam size comparison. There is no current off the shelf suspension/drive system that will work. Not only are the beams the wrong size, but they run on the wrong voltage, with the Mark VI running on 600vdc and the Innovia 300 running on 750 vdc. Then there are questions about load bearing of the WDW beams being too small for the 300 system, and the fact that the 300 system simply won't fit in WDW stations.
Disney may end up buying all new monorails, but they won't be based on the most current and advanced system like the Innovia 300. Instead they are probably going to have to beg Bombardier to go back and build the trains they made for Las Vegas in 2004, either called the Mark VI-M or the Innovia 200 Monorail (yes, I know, they use 200 for something else now, but they used to use it for this). Those trains were essentially the Mark VI, and they were the last commercially available trains to run on the correct beam, as the LV system was based on WDW and even originally used repainted Mark IVs Disney sold them.
Unfortunately those cars for the 2004 LV monorail are neither the most up to date, nor the most reliable of monorails, suffering all kinds of problems that delayed the system 2 years.
How much is Bombardier going to throttle WDW for to get them to go back and build to old tech? I'd say Disney could go in with the LV monorail and do a larger order, but that system has gone bankrupt twice and probably is not looking for new trains...
Rock and a hard place for Disney.