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.
Every phone with removable I had had a pretty flimsy back cover that started to crack during the lifetime of the phone. The gaskets started to go or weren’t even there in the first place, so they weren’t even splash proof (so better avoid getting rained on or even get sweaty).
And none of my phones ever required a battery replacement during its life time. My Galaxy S4 mini ram out of support, I flashed it with a custom rom then that stopped being supported (and the hardware really couldn’t deal with later android version). My Fairphone 2 started crashing regularly which ended its life. And my iPhone 6s had a solid 5 year life with no battery issues before I retired it to get a better camera.
So for me requiring every phone to have an easily replaceable battery has pretty much zero upsides but a bunch of potential downsides.
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.