It had been in the works for a while, but now it has formally been adopted. From the article:
The regulation provides that by 2027 portable batteries incorporated into appliances should be removable and replaceable by the end-user, leaving sufficient time for operators to adapt the design of their products to this requirement.
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.