Imagine… a 3+ day battery if the battery thickness would increase to make the back flat.

Thin phones are NOT the future, long battery life is.

I think there is a possibility to have a local client using Gmail, with a rule set to delete mails on Gmail as soon as they are synced locally. So in this case Gmail would be nothing more than a relay/proxy, while your mails would actually be offline.

Because 99.9% of population doesn’t know what sideloading is, let alone where to find apps and how to sideload them. So, realistically, there isn’t a need for it. Also, Google apps tend to be free with IAP, so no matter where the app comes from, it can still generate them revenue. On Apples side, their apps are mostly paid once upon purchase, so enabling sideloading would effectively cut revenue.

It’s not that people ignore it, it’s just that they don’t really have an alternative. You can rent from Microsoft or Apple, or go the Linux way where you don’t have the proper UX an average user needs and is accustomed to with Windows or macOS.