Why are these installed in /pim/kcms/akregator instead of eg pim/akregator/kcms to have every plugin related to akregator in the same folder? looking at the plugins folder, there's no unified location or naming scheme for plugins. kdevelop chose this solution.

Also, some use the application name (okular, plasma...), others the desktop file name (org.kde.kdecoration2, org.kde.kwin.scenes). Is there an effort to harmonize things?

to have every plugin related to akregator in the same folder?

The plan is to be able to use KPluginMetaData to load the KCMs in Kontact. The KCMs in akregator are not only for internal consumption, that is why I decided for pim/kcms as the prefix. If they were only internal I would agree with your point.

I did the same for some other PIM apps and Laurent reviewed the MRs and did some changes with the same pattern.

Is there an effort to harmonize things?

Yes, so that we can load the KCMs in Kontact using KPluginMetaData and get rid of KServiceTypeTrader & its plugin loading. This is planned since late 2019.

and for the naming scheme?

You mean for the individual plugins? That can be freely chosen as long as it is unique. Ideally it should be the same as the filename of the plugin, but that was already the case here.