Canonical said that it would not support Nexus 5 devices just yet, but that doesn't mean that the community must also follow its lead. A video has popped online showing Ubuntu Touch running on a Nexus 5 phone.Porting Ubuntu Touch for Nexus 5, which has different hardware from the current Nexus 4 supported devices, would force Canonical to make some serious modifications, dislocating resources from the ongoing project.
On the other hand, this shouldn't stop the community from picking up the slack and from doing the work themselves.
As you can clearly see in the video, Ubuntu Touch runs pretty well on Nexus 5, but the size of the display makes the OS think it's on a tablet. The developers, at least this is what the guy in the video says, will fix this problem with a patch soon.
Besides some basic apps, the normal functions of the phone are not working, like the dialer. The radio module is still from Android 4.4.2, but this might get fixed in the next few weeks.
A tutorial has also been posted, but it's in Italian.