> Replacement batteries for any model will have to remain available to users for at least five years after the last unit of the product is placed on the market, the regulation also states.
While standardization would be nice, I can still order batteries for the Samsung phones I've used 15 years ago. Availability might not be that much of an issue with larger brands.
There's an aftermarket for phone batteries. They're new batteries produced by what I imagine are unaffiliated manufacturers. As long as the phone is popular enough, there should be enough market for manufacturers to make new batteries.