Though the use of plural pronoun is grammatical for the indefinite pronouns such as somebody, someone, anyone etc., it sounds meaningless to me. For example, somebody is knocking at the door. I know that only one person is knocking at the door.
But I have to say "Aren't they*?" in question tags and other uses. Though the use of plural pronoun may solve the gender bias, linguistically it sounds meaningless.
What is the problem if we use the pronoun "he" in its place? The issue of gender-bias tarnished English. Other languages have not made changes like this.