Actually they port the Nexus 7 factory image that is android Marshmallow 6.0 to Nexus 4 code name Mako device.This Rom is Stable and can be used as a daily drivers.there may be some bugs as it is not the official rom.
Tested & Working: sensors,
NFC, WiFi, Bluetooth, Camera, Cell, GPS.You can Download then Android M
rom for Nexus 4 from the link given below and follow below Guide on how
to flash Android Marshmallow rom in Nexus 4.
#How to flash Android Marshmallow 6.0 on LG Nexus 4
1.Download Android Marshmallow 6.0 Custom Rom for Nexus 4.
4.Now Extract the Android M 6.0 Rom that your downloaded from step in Mfastboot drivers.
fastboot erase system
fastboot flash system system.img
fastboot erase boot
fastboot flash boot boot.img