I think you’re assuming that the new phones have to be hot swappable. They don’t, they just want it to be relatively easy for someone to do with a screwdriver. The phones can look virtually identical to the way they look today with the exception of a couple of non proprietary screws. This would be no more of an obstacle to water resistance than a button.

This is not a requirement that people can hot swap the battery while they’re out. It’s just getting rid of the egregious obstacles like glue or hiding a battery behind a bunch of other parts or using different types of screws.