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.
Personally, I find that this “sleekness” was misleading anyway. What was the first thing most people did once the “sleek” era started? Bought a case, sometimes like an OtterBox or knock off. That tripled the thickness of many phones, and even the most basic protective case came close to doubling the thickness. Back in the “old days” of slide out keyboards etc, the phones themselves had a decent case built in, so the “cases” were more fashion statements. And anyway, it’s not like the Note 2 with a plastic back you could pop off was especially thick at the time. Honestly - a lot of the “problem” is intentional design to force buying new ones I think.
Look at ultrabooks - Lenovo proves with the X1 you can have an easily removable bottom using gasp metal and screws. Yet still be very thin. I honestly think the better solution for phones is just to have the battery be click on / external like power tools, drone batteries, older laptop batteries. The back of the battery is the back of the phone. There’s no reason the contacts can’t be press fit on the back of the phone and front of the battery - i.e. it doesn’t have to be especially thick / deep.