The waterproofing has been solved, but the real issue is that device size and/or battery capacity is going to be affected. And with the resiliency of modern batteries, you’re making design sacrifices for something that won’t affect most users.
Sure, it was nice being able to swap a fresh battery in on the fly. But these days you can also just get a decent power bank for less money than a proprietary battery pack.
A middle ground would end up being better for everybody. Keep the batteries as they are now, but make the phones a bit easier to open (and use fasteners instead of adhesives).
If you want some really wild old storage tech, a normal VHS cassette could hold 3-5gb of data. But we didn’t have any use for that much storage at the time, and CDs were taking over by the time we did, so nobody bought the VHS storage hardware.