Last week, the WordPress code development team announced a new theme template in WordPress 4.3, singular.php. According to the ticket that was opened on June 18, 2015 - that resulted in the new them template being created - this was due to singular being the only template context conditional that didn't have a corresponding template.
In terms of the WordPress theme template hierarchy, the core development team stated that singular.php comes after single.php, page.php, and the variations of each.
WordPress 4.3 is currently still in development, with beta 2 being released on July 8, 2015. The production ready version should be released soon.
