Upstream has released version 5.3 back at the end of August, with bugfixes for issues in previous releases[1]. A simple renaming of the ebuild file itself is all that's needed. The renamed packaged downloads and builds the sources without issue. The files I used to test his are available at [2]. Testing the built program, I can't find any new errors or bugs. 1. https://community.ardour.org/node/13901 2. https://github.com/Korethr/Portage-Overlay/tree/master/media-sound/ardour
I bumped the ebuild to the new version now. Thanks Jeremy!