I think there's no plugin available or a recent fork of Elgg that would provide any federation functionality or the option to connect different "nodes" of Elgg sites. Elgg is no distrubuted social network framework. Each site is basically a stand-alone social network site. I guess it would be possible (with more or less effort) to create a plugin that uses some available protocol to share content between different sites. But nobody seems to have written such a plugin so far (or at least not published it to a wider audience).
info@elgg.org
Security issues should be reported to security@elgg.org!
©2014 the Elgg Foundation
Elgg is a registered trademark of Thematic Networks.
Cover image by Raül Utrera is used under Creative Commons license.
Icons by Flaticon and FontAwesome.