I think "Go Live" on discord has rolled out to everybody now? Join a voice channel, hit the button (next to Disconnect) and pick an app or screen. Needs Nitro for good quality (otherwise you're stuck at 720p). Latency is better than most other streaming things I've tried.

100% agree on the other two, though. Encouraging people to make channels as needed helps the first, but for ephemeral discussions you wind up deciding between deleting the chat log, or living with a lot of "retired" channels. And being default opt-in for notifications makes Discord _way_ more noisy than Slack could ever be.