I was following the Aether guide here:
http://wiki.eclipse.org/Aether/Using_Aether_in_Maven_Plugins

But instructions in that wiki made the plugin break (actually that's how I discovered issue) due to:
https://jira.codehaus.org/browse/MNG-5513

Temporary solution was to set scopes to "provided" (that is the opposite what wiki page proposes), and that would break in 3.0.x anyway, as Eclipse Aether is NOT provided with it.