@hiccup writes on the forum:

In Picard's settings panel you can set to use ID3v2.4
Doing that enables the option to use UTF-8 instead of UTF-16.
But since UTF-8 is the preferred default for ID3v2.4, shouldn't it also activate UTF-8, instead of making it an option?

If this is done, it should probably also have a function for migrating configuration files somehow, so people who previously had the option unset will get the "new" option set so all their files don't suddenly change character set. (So maybe hold off on this until 2.0 where there will be a lot of other changes anyway?)