I expect smartphones to look more like the Pro Controller tradeoffs than the joy cons. The issue with replaceable batteries is you need the extra space for the battery structure so unless phones grow they'll have lower capacities. There's also IP ratings, phones have pretty good IP ratings these days often surviving drops in puddles etc where none of these products have any official IP rating to preserve when adding doors etc for replacement batteries.

I'm baffled that we still are thinking that we want thin phones. We have a gigantic camera bump that would be removed if the phone was thicker. Who wants a razor in their pocket, like really?