I was now able to discuss the current state of DDE development in more detail directly with Hualet Wang of Deepin.
Their current focus is on the next release v20, which apparently will bring a lot of changes beyond regular package updates.
This means that fixing issues for existing installs - at least Archlinux-based ones - would be a lot of extra effort for them and is unlikely to happen at all.
I must admit that, from their point of view this is understandable.
Hualet also tells me that after the v20 release, a release cycle more compatible with rolling releases will be an option that Deepin might pursue - but this remains to be seen.
Conclusion for us at the current moment:
Providing install media with a mixture of old and half-baked newer packages at this point in time makes little sense, especially when we cannot expect issues to be fixed at all and the prospect is a possible complete breakage with the final release of Deepin v20.
We will now just have to wait for this release and then see where we can go from there.
I will stay in contact with both Deepin and the Archlinux packager to try and find ways for a continued maintenance of DDE on Archlinux-based distros in general and for Manjaro-Deepin in particular, which is still quite a popular edition despite it has been such a harsh ride for quite a while now, already. This makes it obvious that people would really like to be able to use this desktop on Manjaro...
to be continued