Not only there are multiple plugins that do this now, this is something that was explored by Google itself back in 2009 with Google Sidewiki[1].
Edit: I was genuinely asking because I had not heard of similar solutions prior to today. But go ahead and keep downvoting me. That'll teach me to engage in honest conversation.
Those aren't the same thing, after all. The echo chambers of self-described dissenters often seem little different than those they claim to dissent against.
It’s sad that it’s associated with a political faction, though Torba’s statements make it clear why. Gab actually has (or had, it’s been over a year since I logged on to it) far superior stream filtering tools to Twitter.