I know this is a niche of a niche, but are there any known systemd-boot + nvidia driver builds or configs anyone can point me to?
I wouldn’t be dissuaded from having to do one myself, just wanted to kick the tires on one if it was already out there.
I’m with you on wanting a robust, atomic system with systemd-boot 
I highly prefer systemd-boot myself over GRUB for its simplicity and ease of use. Unfortunately ostree itself doesn’t systemd-boot support yet.
I don’t think a good BTRFS snapshot rollback integration with systemd-boot even exists yet, if any. This EndeavourOS forum thread for example has someone sharing their workaround to get snapshots bootable from the systemd-boot menu, but that needs workarounds for /boot to keep the snapshots bootable after a kernel upgrade. There’s snapper_systemd_boot on GitHub, but it doesn’t seem to be alive.
It seems openSUSE microOS is working on it for Aeon’s release, there’s a link to openSUSE’s progress down the thread. It will be interesting to see its development!
But also. . . systemd-boot support · Issue #1719 · ostreedev/ostree · GitHub
I wouldn’t use BTRFS. I’d be using LVM+XFS.
BTRFS is just not my cup of tea, seeing how many issues with ro mounts , games and others, also distros not having a native solution to integrate Snapshots as it’s main feature amongst other things.