It does not support trimming implicit self either, so would be good to have both options.

Adding or removing explicit self would likely require semantic information about the symbols, not just the syntax, to distinguish identifiers and know whether they're members of self and that the code could be changed without changing its behavior.

It might be possible to approximate it by tracking symbols in their lexical scopes and use that to determine which symbol is being referred to, we wouldn't have access to the compiler Decls that would let us be 100% confident that self is the same as the container for some property x if it's also in the presence of other shadowing names.

FYI SwiftLint has a semantic version of this https://github.com/realm/SwiftLint/#configuration and SwiftFormat has a best effort version where it inserts and removes only ones it's confident about AFAIUI

Closing this as not planned, since we would need semantic information to do this correctly, and I prefer not to implement a syntax-only version that is incomplete.