Start a thread with one tap.
There are always opportunities to improve user experience, even within core features of best-in-class products. Slack's utility has allowed it to fundamentally transform team communication, and its ubiquity has played a major role in its ability to do so. Of all the mediums through which we get work done, we have the most intimate and unforgiving relationship with mobile. Though Slack's app currently allows users to reply to a message as part of a thread, I believe the UX therein can be more seamless.
This project was completed as part of my application for the 2018 KPCB Design Fellows program.
Tools | Sketch
The current design of Slack messages on mobile does not permit quick use of the "Start a thread" feature when appropriate. Before a user can type a threaded reply to a message, they must first tap the message, and then tap the "Start a thread" button on the next screen. Because this requires two steps instead of one – as well as an acute shift in cognitive focus – many users opt to create a new message when starting a thread is actually more suitable. This leads to clutter, as channels quickly fill up with unthreaded messages that are really part of the same conversation.
Rationale & Recommendation
In providing this recommendation, I acknowledge that it is blind to usability requirements, product roadmap considerations, and other constraints that Slack's design team may be managing internally.
Based on my experience using Slack and my understanding of human communication, I believe that most Slack threads and most message sequences that should be threads, begin with a question from a member of the channel. Ideally, I would want to verify this assumption with more data and empirical evidence – but in the absence of adequate time and resources, I will proceed assuming it is true.
If it is true that most threads begin with a question, then I recommend placing a "Start a thread" button next to each question-containing message in the channel. Tapping this button should also allow users to reply to existing threads, so let us refer to it as the "Start a thread/Reply" button going forward. To avoid excessive repetition in the UI, the button should not be placed next to messages that don't contain questions.
The updated design allows users to start a thread or reply with one action: tapping the "Start a thread/Reply" button, which appears, conveniently, to the right of the message content. After the button is tapped, the user can immediately begin typing a response.
This results in cleaner, more digestible channels, as messages that are part of the same conversation are grouped under a single thread.