Could pair Mumble with Discord, but I think the days of people being okay with having a different app for messaging and voice communication is over (when it comes to gaming surely) after a post-Discord world.
Also, as much as I love Mumble and its voice quality (and low latency), Discord is much more plug and play. Mumble needs microphone specific fine tuning to work well. Which is worth it for me, but is nothing you can quickly get someone else to do.