I don't know if you ever see the ifixit tear downs, there is no new tricks. The battery is still replaceable, it's just that the manufacturing process adds more stuff to "anti-tempering". Let me list a few:

• special kind of screw, some screw can't be unscrewed without special screw driver
• we all know about glue battery so they are fixed in place AND harder to remove safely.
• they add more of those tiny ribbon around so if you don't know the internal layout there is a chance you break the ribbon.
• plastic wedge that might be broken when you try to pry it open(so when you put the cover back it's a bit loose, and lose water resist), even with proper tool. They designed it so it was not suppose to open again. ( I have a old casio slim camera that can still be water resistant with removable battery, there is no reason why a phone can't do the same with modern materials. )

there are very few people who would prioritize a replaceable battery over other features.

I gotta gently push back against this. You may not know them personally, but there are a LOT of people who have gone back to dumbphones over this. IMO, this is a large part of why dumbphone sales are catching up on smartphone sales for the first time in years. I even know some elderly folks who stopped using cell phones entirely when smartphones stopped having replaceable batteries (easier going back to having a landline when one is retired/not raising kids, of course).

There are very few people who buy the currently existing smartphones who would prioritize this feature, yes -- because anyone who does prioritize this feature has been excluded from the entire smartphone market for several years now.

Please tell me what new design / feature precludes an easily changeable battery? The only one is supposedly the ever slimmer form factor, which is IMHO not actually that wanted because everyone I've ever seen immediately adds bulk back with a case. If the phone was a little thicker, more tough, and not glass all around, I could see people going back to not needing a case.

I think it's extremely hard to tell what people would prioritize. If you aks them hypothetically, everyone probably is some green warrior for mother earth. But then when push comes to shove, the industry will give them the choice between a flagship phone, glued all around, and a phone with a removable battery with all the greatest specs from five years ago. Of course many will chose the glued one, and then some people will be like "welp, the free market has decided". 🤷

edit: typo

The Samsung Galaxy S5 was a good example of this. The back panel and battery was removable, and the charging port had an extra plastic cover that went on top to protect against water ingress