The github issue that you linked offers a possible solution to integrating WMTS, I am not aware of another. There are currently no plans for further feature development for Neatline for Omeka Classic due to our focus on developing a Neatline module for Omeka S. WMTS integration has been suggested to developers as a possible feature for the future Neatline module for Omeka S. We do not currently have a release date for a production version of this module.