My hypothesis is: Apple will enable the reverse wireless charging feature in the iPhone for AirPods 3 and Pro sooner rather than later, maybe through software update down the line, or maybe in the next generation of iPhones (Sept 2022) at last.
Otherwise it makes no sense to me, it's not difficult by any means to place one of these charging cases aligned with the coil inside any Qi charging pad – including Apple's own MagSafe charging puck. MagSafe will enable a perfect alignment if you have bought the puck already, sure, but the charging case only demands 5 watts of power with no fast charging capability whatsoever, the imbedded magnets provide no meaningful benefits in this case. (sorry for the pun)
The more I think about it, the more I tend to believe that these charging cases are not primary intended to work with the charging puck, but to work with the iPhone. Because not every iPhone owner would buy a MagSafe charging puck, but every AirPods owner guaranteed has an iPhone! Forgot to charge the AirPods charging case last night? Simply snap it to the back of your iPhone and you're good to go. It starts to make perfect sense now.
Considering that iPhone can already reverse charge the
MagSafe Battery Pack, albeit the iPhone must be plugged in and charged above 80% because of obvious reasons, the AirPods charging case is basically a shrank-down version of that, I'd be surprised if Apple gives these charging cases the MagSafe compatibility then does nothing with it and walks away.