What's the difference between an individual AirPod and a cordless drill battery? My cordless drill takes a li-ion battery stick, which is itself enclosed in a sealed, rugged ABS plastic case for safety and durability. The case also contains a thermal sensor, on-board processor chip, fuse, status LEDs, and electrical contacts. AirPod: add to that a relatively inexpensive earbud driver, microphone, and an IR sensor. Consider the AirPod itself is much the same as a cordless drill battery.
The charging case, now perhaps having a replaceable battery there would be doable, though such changes might have other consequences in size and durability. It is already bad enough that dropping the case with AirPods inside onto a tile floor will often result in the lid opening and the AirPods flying out. At least they don't also all fly apart or break. I'm amazed at the durability, having dropped mine onto concrete and even stepped on the AirPods themselves unintentionally!
It's tempting to suggest Apple could simply make the AirPod stems threaded (ideally with elegant and tiny threaded inserts). That would be doable, but you still have to route the connections for power and microphone somehow, or perhaps move the microphone up into the earbud. Same for the antenna. If it's going to be user serviceable like that, you still must protect the user from puncturing or shorting the battery or mutilating any other delicate bits. A non-soldered contact for power (and any other signals) is also a failure point, especially if dirt or water could find its way there.
Samsung's solution is interesting. Time will tell if a) it's durable/reliable enough, and b) people actually replace the batteries. If your design fails at durability and reliability, you've done the environment no favor. If people don't replace the batteries, you've wasted manufacturing energy and possibly caused (a) unnecessarily.
Engineering and product design are full of difficult compromises.
