Nothing should ever be "expected". Disney, in no way, shape, or form promises the monorail or any other item on their property will always be 100% operational. They try, but exceptions arise, and it's people with an attitude of "if something isn't perfect or operational the way I want, then I will complain and moan that my vacation was ruined" that give Disney the reasoning to not do regular refurbs. Besides, they inform guests about the delays so expecting something to be open, when it isnt, is on the guest. Disney made the effort.
I'm going to push back just a bit on this one. When I book a flight from Washington to New York, I expect the airline is going to fly me on an airplane - not load me on a bus at the airport for my journey. Sure, the bus gets me there, but if I expect a flight, and I pay for the flight, I expect to be flown on an airplane not loaded onto a bus. Informing me of the airplane-to-bus change after I paid for a flight is unacceptable. However, if I was told prior to booking that service from DC to NYC for a given period of time were going to be by bus instead of plane, I would not book my flight for those times...or I would go ahead and just book a cheap bus instead of paying the higher fare.
This isn't like an attraction being down or anything like that. Disney markets GF, Poly, and CR as Monorail resorts. Monorails are the primary form of transportation for the resorts, are part of the resort infrastructure like an elevator, toilet, air conditioning, etc, and as such should be expected by any guest paying to stay at the resort.
The Monorails aren't a form of entertainment that we should expect to go down for refurbs from time to time. It is a transportation system. All transportation systems need investments for upkeep and upgrades, and this seems to be one of those times.
I am happy that Disney is investing in upgrades for the Monorail system. It needs it. I hope it comes through the other end of the upgrade period in much better shape than it went in. At the same time, I would be angry if I was staying at a resort where the Monorail was the selling point, only to learn of a diminished capacity and capability of the system during my stay. I would likely ask to be moved to another resort elsewhere on property. If EPCOT was my thing, I would ask to be moved to Boardwalk/Beach Club/Yacht Club. If MK was my focus, I would ask to be moved to CR so I could walk to the park. And I would demand the difference in price be refunded.
The availability of the attractions in the parks is always a variable - you can't rely on all the attractions being running all the time. The transportation systems, however, can't be a variable. If I have an 8 AM dining reservation at EPCOT, and I am staying at the GF where the Monorail is the primary form of transportation, I expect to be able to walk down to the platform and board a train to get me to my destination. If Disney is unable to accomplish that...I expect to have had plenty of warning PRIOR to booking my vacation.