@jonahstein @jerry @ssb I think I see what you mean. All the masto UIs I've used really suck at threading (if they can at all). The Elk UI doesn't do a bad job of it.
I've just started learning ActivityPub and have been experimenting with writing bots and a new federated service, and am just starting to get an understanding of how messages get delivered to endpoints, etc.
I imagine with masto's incipient popularity we'll see more front-ends and other options. Pretty exciting. :)