There won't be new monorail vehicles by 2021. As soon as I heard that Bombardier was given the contract, I knew wdw would be looking at a decade before delivery. Do a google search of Bombardier and you'll quickly see the legal trouble they are in for not delivering on their contracts all over the world in the past decade (London, Toronto, Waterloo, Switzerland). And it's not just being months late on delivery, but
years late. They are so far behind on their contracts in these cities that it will be years before they can even start on wdw.
I'm surprised that anyone is still hiring them, but I guess when only a few companies in the world can make these vehicles, there is basically no competition.