That's assuming there's as much of a market for second hand keyboards as there is for second hand iPads. Someone who buys a second hand iPad could decide that their use cases don't require the Apple Magic Keyboard, or that if they want to get a Magic Keyboard, they'd be better off getting the more recent model.One cannot not ignore the opportunities though to complain about each option.
Scenario 1:Waaah, it's not compatible - woe is me!
Scenario 2: Waaah, it doesn't support feature x and iPads are too thin. Woe is me!
Sure, you may eventually get someone to buy it off you, but you'd have to take a much deeper cut on the selling price to attract a buyer, and you might decide it's not worth it. Either way, it'll create some friction that'd lead to some unused Magic Keyboards.
As many people have said here. the 0.5mm difference doesn't constitute enough to stop the iPad from closing, so with that in mind, it'd make sense to not use software to stop the old Keyboard from working with new iPads, even if Apple itself chooses not to sell the old Keyboards any more.
When all's said and done though, I remain skeptical about this story until I see the proof from Apple itself, especially as I had this interaction with their agent.