For the record ... when I do a fresh install of Sigil from the repo on Xenial (I set up a VM), and install the test plugin, the error I get when first trying to run the plugin is: "Error: Interpreter Python3.4 has no path set". Which is sort of what I figured.
After using the Plugin Manager to set the Python 3.x path (the 'Auto' button set the path to /usr/bin/python3 for me) the plugin then passed all tests with flying colors! Yay! Full Sigil ... plugin support (with all the recommended extra python modules) ... no compiling, no pipping.
On a completely unrelated note ... I'd forgotten how badly I hate Ubuntu's Unity interface.
