Given they are currently refurbing them, again, they are clearly planning to have the same ones running for a while. Let's face it, a replacement of the current trains would be a several year process anyway. I'd assume this refurb is to provide at least a 5 to 10yr lifespan for some of the current stock. Even if the contract were signed today, it would be a year or two, at least, before first delivery of a single train and then probably 6 months between each delivery at minimum. I'd assume they are trying to buy several years before having to sign that contract and then to cannibalize older trains to keep a few running over the long replacement process.
Of course, the options for replacement are interesting as well. Do they reuse the running gear and just replace the cabins, as they've done in the past, or do they go completely new trains bottom up? If completely new trains, do they shut down the system for a year or more and upspec the electrical to work with a more modern system, even if the beams are still a limiting factor? There are pluses and minuses to that idea for the long-term. Then there are amenities, such as do they build in onboard electrical storage for emergencies?
Who knows? But I suspect the ongoing refurb is designed to buy them 3-5 years before a contract needs to be signed, and 5-10 years before replacement is completed. In my opinion, part of the reason all this was so delayed was the automation upgrade. If they hadn't been so focused on having that much overdue project finished, tested, and ready to go for the next generation, I believe the contract would have been signed 5 years ago. However, that project, by all accounts, was late and not particularly smooth in implementation, so it pushed things back.
And now here we are with a whole new set of impediments to large infrastructure investment. Especially the kind of investment that isn't really going to drive much new revenue. A new ride has definite payback. While there is a subset of Disney folks who will come and spend money just to ride on "new" monorails, it's a lot smaller than the subset that will come and spend money to go on a new rollercoaster. It's just not as sexy, though very needed. And when all this COVID stuff ends, Disney is going to need sexy more than they need new monorails to get people visiting again in the numbers they had in 2019...