I think 90% chance of apple going for the EU-Specific model just like they did for Digital markets act, 10 chance of screws, 0% chance of actually popping the back cover off with bare hands.
For Samsung, 50% chance EU-Specific models 40% chance screws, 10% chance back cover tool-less removal. (Edit: typo)
As for other smaller manufacturers, probably just 50%/50% either screws or tool-less back cover removal.
I used to carry 2 batteries. Though that’s probably not a large market. But if made around that idea it could be done well.
Either having hibernation or some power source to keep the RAM powered during main battery swap (small supercapacitor, small regular Li-Ion battery, thin lithium ceramic battery, I don’t know what’s best), and a dock for battery charging.
Kind of like LG G5.
Preferably, the battery would have integrated charger so you don’t have to carry around a dock. Just what you do now, just with the spare battery replacing a power bank in more convenient way. Maybe it could come off with the charging port just like LG G5, but it would be built-in rather than being something you pop a different battery into.