It's about rust conversion as far as I can tell (slide 15 & 38), but not sure why Proxmox is an example. There is no recording of the event and the speaker notes have nothing about Proxmox, so I'm not sure if there is any kind of connection.
One...
Not a GUI plugin as that is not possible right now (AFAIK), but a plugin exists that integrates bcachefs with Proxmox. See my thread: Bcachefs storage plugin for Proxmox VE