There is always a second filter bubble. In the case of non-federated sites, that filter is in the form of the policy of the site and also the algorithms used to sort feeds and replies.
With federated solutions, users have a choice.
With federated solutions, users have a choice.
Twitter is fairly lightly moderated I think, and the "following" tab gives a raw timeline.
If federated services pick up steam, they will pick between a few popular options.