So there's going to be a catch here and I'm curious how it will work out. Integrating the battery directly into the phone without it being easily removable is going to mean less capacity since the battery will need a heavier-duty shell since you can't rely on the phone itself for protection. I get the e-waste angle but generally I wouldn't keep a phone past the end of updates anyways, and usually battery life is still acceptable at 4 years with good practices (not charging to 100% and holding it there overnight, etc).
My last two phones both got slow as their batteries got bad, and were basically like new after replacing them. My current phone doesn't allow swapping the batteries.
For someone thrifty, being able to replace the battery can extend a phone's life 2x or more. Even if you don't want to keep using it, you could still resell it or give it to someone who doesn't need the newest phones. Non-swappable batteries are a form of planned obsolescence, in addition to just being more compact and probably a little cheaper.