The European Union is working on legislation that would require smartphone design to have easily replaceable batteries, but we doubt Apple would agree willingly.
I’ve commented this elsewhere but it wouldn’t surprise me if they actually over engineer the replaceable battery and incorporate their MagSafe tech or something to make replacement batteries prohibitively expensive but technically follows EU rules. Seems like a very Apple malicious compliance outcome.
The first thought that came to my mind was internal solid state power storage (good for an hour or so, but will outlive the rest of the phone) with an external MagSafe battery. Call it MC, but that’s definitely a more Apple UX than disassembling your water resistant phone.