We keep finding cases where the recipient's gender is needed (primarily for French messages). For Thanks notifications the recipient is also in the extra event data, but for mentions it's not. There should be an accessor exposing $this->user (or the recipient for gender purposes, if we want to support that being different from the user for permission checks purposes for some reason).
Related Gerrit Patches:
|mediawiki/extensions/Echo : master||EventPresentationModel: Add accessor for current user's username|