Even if Nexus 5 has been available for some time now, support hasn't been confirmed
The Nexus 5 smartphone has been release by Google for a while now, but Canonical hasn't said anything yet about officially porting Ubuntu Touch on the new device.There is a big community of developers who are already porting Ubuntu Touch on a lot of other devices, including Samsung S4, for example. Other less known devices will also probably get ports soon. So far, there is no word about officiall support for Nexus 5.
When Canonical first announced Ubuntu Touch, almost a year ago, they said that it would run on Nexus and Nexus 4. The list has been expanded to include Nexus 7 and Nexus 10.
As it stands right now, the only platform being actively developed is the Nexus 4. This is understandable because they have to focus their efforts on a single platform, but at least we know that they intend to make the operating system available on the other devices sometime in the future.
This means that Canonical is doing the actual work and it’s not leaving the development for third-party parties. It would stand to reason that Nexus 5 would be high on their list, but questions related to this particular subject have remained unanswered on the official mailing list.
Let’s hope that Canonical will not delay the adoption of Nexus 5 in the Ubuntu Touch family for too long.