It would be nice to if users could prove that their identity on https://keybase.io/ is connected to a soundcloud user account. It provides a way to cryptographically verify an account (the keybase user) has ownership of another identity, in this case soundcloud. That keybase user can then prove ownership of other online identities as well like twitter, reddit, github etc to establish a strong connection between all these.
Here is keybase's guide on how to integrate: https://keybase.io/docs/proof_integration_guide
This is slightly related to but probably not dependent of Add ActivityPub Support to Soundcloud