I don't see how this should in any way affect:
1. the current and continued development of owncloud,
Most of their developers (if not all) left and started their own new project (open source). And their creditors (banks) pulled credit support. So owncloud lost their devs and their cash. It is unlikely that they will recover. Most users will eventually move onto Nextcloud.
If I were the developer of this container, I wouldn't put more effort into a project that is on its last leg. Keeping owncloud up to date has always been a struggle, even on a vanilla ubuntu install that I myself experienced, I can imagine it would much more complicated in a docker container. I can't speak for the dev, but if it were me, I would advise users to move onto Nextcloud. And if I wanted to continue maintaining a container for file sync & share, I would start working on nextcloud, but that's just me