It took far too long, but I've finally posted a 7.x update for project Node Theme at https://drupal.org/project/node_theme. 
Node Theme is used to control which theme a given path will use. "Node Theme" is a bit of a misnomer, a holdover from 6.x. It can be used to record the theme choice for any path on the site, and will seamlessly switch the rendering to that theme when the page is requested.