@tom I guess you will have to install/flash complete ROM for cm12.1 on Nexus 5 and then reflash Ubuntu OTA12 or latest rc-proposed on it.

@apple-muncy : Here are the links:

http://news.tecmint.com/aethercast-arrives-on-the-nexus-5-oneplus-one-support-in-tow/
http://news.softpedia.com/news/wireless-display-support-is-coming-to-nexus-5-and-oneplus-one-ubuntu-phones-504915.shtml

I went by the statement "This build is based on the ubp-5.1 branch (android 5.1/cm12.1)" and tried Android5.1.

But I think I should have tried cm12.1: https://forums.ubports.com/topic/15/what-is-ubp-5-1-1

@tom : My understanding is that the ubport software updates don't change AOSP stuff, at least not on nexus 5. @mariogrip can you confirm this?