Hi all. As promised, I have released the following build to the wide world:
lineage-13.0-20170212-UNOFFICIAL-libra.zip available at:
https://drive.google.com/drive/folders/0B6syT4ByVmXsN21KYldYUFFaUFk
Device source:
https://github.com/calroth/android_device_xiaomi_libra
Kernel source:
https://github.com/calroth/android_kernel_xiaomi_msm8992
Based on: @ketut.kumajaya's sources, with inspiration from @emfox. And dozens of others. Thanks to you all
Now, some important notes:
Standard disclaimer: there is no warranty. Back up your device first

If you find this ROM unstable, let me know! Then revert to the ROM of your choice
Contains radio firmware from MIUI V8.1.3.0; will automatically update your device when you flash
There is no root (su) access. This is how LineageOS comes these days (source)
All proprietary blobs are from official MIUI V8.1.3.0, except for the "gatekeeper" library which is from official MIUI developer V7.1.20
Tested with TS TWRP 3.0.2-0 from Team Superluminal
Tested with Open GApps ARM64 6.0 Stock
What works and what doesn't:
Works and tested 3G/4G data and voice (a.k.a. the radio)
Works and tested Wi-Fi
Works and tested GPS, including AGPS
Works and tested Sensors (accelerometer, compass, gyroscope etc.)
Works and tested OpenGL-based apps and games
Works and tested Hardware encryption
Works and tested Use of f2fs for /data partition
Mostly working Camera and flash for still photos; seems to work OK but needs more testing
Mostly working Bluetooth works, but sometimes turns itself off; trying to find out why
UntestedQualcomm CnE for quick handoff between Wi-Fi and 3G/4G data
UntestedQualcomm IZat for getting your location using a mix of GPS, Bluetooth, Wi-Fi and other sensors
Broken Camera for video recording; working on a fix
Broken RenderScript, if anyone was using this; unsure if I can get this working or if there's demand
Removed Qualcomm Wireless Display (Miracast), if anyone was using this
RemovedIP Multimedia Subsystem packages, if anyone was using this
Good luck! And thanks to the community.