I think you are missing the point.
First of all, you can rate content, create comments, follow users, create dev logs, create comments for dev logs. I don't know what features YOU need to call it a social network, but itch.io is a social network.
Secondly, no one is asking for multiplayer or any other new feature (other than maybe an opt-in), what I see here is people asking to make possible for apps to access an information that already exists (and is public).
I still don't understand your argument about how making the public usernames easily accessible would be a security concern.
I am not sure if you just want to be against this proposal or you have a real concern, if is the latter, what do you recommend? Oauth? Each game to implement a secondary login on top of itch.io? What would be the safest way to do it?