Based on Android 4.4.2 AOSP sources, you can now flash Android 4.4.2 on Nexus 5 too using the Liscio custom firmware. Liscio Android 4.4.2 custom ROM carries a very stock feel with few enhancements on the top. Here is how you can flash Android 4.4.2 on Nexus 5 with Liscio.

Flash Android 4.4.2 on Nexus 5 with Liscio custom ROM:

Downloadand install USB drivers for Nexus 5in your computer.Enable USB debugging option by pressingMenu>Settings>Applications. Navigateand tap onDeveloper Optionsto ensure thatUSB Debuggingis enabled.Your Nexus 5 should be rooted.Make sure that ClockworkMod recovery is installed.Ensure that your Nexus 5carries more than 70% of charge.

Guide to flash Android 4.4.2 on Nexus 5 with Liscio:

Required files: Download LiscioAndroid 4.4.2custom firmware fromhereon your computer. Also, download GApps package for Android 4.2.2 fromhere.

Connect your Nexus 5to your PC using USB cable and copy the downloaded files to the SD card of your Galaxy device.Disconnect your Nexus 5and power it off.Now boot it in to the CMW recovery mode: press and holdVolume Up, Homeand thePowerbuttons simultaneously. UseVolumekeys to highlight andPowerbutton to select.Nandroid backup: selectBackup and Restoreoption to perform the Nandroid backup of your current OS.Data wipe operations: go towipe data/factory resetand confirm the operation. Alsowipe cache partitionand finally go forwipe dalvik cachetoclean it up too.Now, selectinstall zip from sdcardand thenchoose zip from Sdcard. Locatethe Liscio Android 4.4.2 KitKat file and confirm its installation.When the ROM installation completes successfully, repeat the above step for installing the GApps package.Once done, go back to main recovery menu and selectreboot system now.