On the other hand previous approach with NUnit 2.x was a big pain for us. Whenever new feature was added to new NUnit version we instantly got a feature request to bundle this new version. As a result TeamCity bundles dozens of NUnit 2.x versions, because we can’t remove them anyhow without breaking existing builds. Basically previous approach did not scale at all.
You’re saying that we need to setup a feed to retrieve NUnit. But there is an official feed for NUnit 3.x packages. Seems you can just use it.