A direct address to @finite reef and to those interested (Thank you and your team for the incredible effort in preserving MC's history so far!):
I am the developer for the CraftPresence Mod (https://www.curseforge.com/minecraft/mc-mods/craftpresence), designed to bring Discord Rich Presence across all major (and moddable) versions of Minecraft (Currently a1.1.2_01 up to 1.19.4, and the 1.20 snapshots). Whether it's through Risugami's ModLoader, Fabric, Forge, Rift (At one point), Legacy fabric, or Quilt -- CraftPresence was designed to be there for everyone, as one universal way to show others what you're playing.
Taking a look into BetaCraft's launcher, I didn't see a route to go about suggesting an addition, so I thought I'd ask you personally on whether it can be included in the mod's repository (Note however, CraftPresence is actively maintained on all major Beta and alpha MC versions, so this isn't really a "set it and forget about it" scenario -- updates to the mod do release quite frequently, with their share of bug fixes and new enhancements to the overall experience)
Either way, I'm interested to hear from you, and keep up the good work on BetaCraft and the archival effort in general 😄