Replaceable batteries are coming to the EU in general, at least for portable devices, via the EU Batteries Regulation, which is in force already and requires all portable batteries to be easily removable and replaceable by the end user from 2027

Replaceable batteries are coming back in the EU though due to the battery regulation (EU) 2023/1542 which requires portable batteries to be removable and replaceable

Yes slow charging is one factor to prolong battery life. You can even go down to 5w or less. But another important factor is not having your phone charged at 100% for long durations, because at high voltage the battery degrades faster. So don’t leave your phone plugged in when it’s fully charged, try to keep it between 30 and 80% all the time for maximum lifetime