I think apps would need to be rewritten from the ground up with ActivityPods as a basis instead of every software’s ActivityPub implementation. Very interesting technology and it definitely does solve a shortcoming that the Fediverse tends to have at the moment. (Mastodon sorta has a SSO implementation of its own but other services lack it and it’s quite the issue). But I am afraid most Fedi developers won’t rebuild their apps just for this.