Minor update, this week's Horizon mobile app update seemingly added a flag that will allow people to show their Discord on their main profile page.
There's also a new deeplinking flow in the HzOS social layer that may allow people to join games via invites within Discord.
Discord's most recent Android builds now detect if they are running on a Quest device and give the option to login via the Horizon app, though I couldn't get it working just yet.
Voice input also works now. Previously, there were issues with the microphone/calling permission.