Introduce the feature you want to discuss: Visibility/Privacy options for profile data fields. The only field that needs to be public is the account name. All other fields could technically be private (or only visible for followers or only visible to other users on the same instance etc.)
Background to problem: Currently one could crawl the public API endpoint for accounts from each instance and harvest a lot of data from the profiles.
Alternatively you might be able to use a random key for identifying users In the API to make it harder to crawl the accounts endpoint.