I'm all for replaceable batteries, but in practice I think they create more safety issues. Many users with old phones will choose the cheapest replacement available, and quality of it will likely be worse than of those shipped with branded phones.
Just look at any grocery store checkout aisle or pharmacy, and see dozens of standardized battery sizes, from AA to 9-volt, or literally dozens of sizes of button cell batteries.
If they were standardized, then rather than going to Amazon for the cheapest Chinese knockoff that mentions your phone, you'd go to the local Best Buy or whatever.
Unlikely to happen. It's one of the few places that phones can differentiate themselves so manufacturers are unlikely to want to lose that option to tinker with.
I don't think you can claim that non-replaceable batteries are a clear safety issue, especially when the replacement market would be flooded with cheap junk hand grenades.
