As mentioned on irc:#kde-devel, kipi is now unmaintained (digikam who used to maintain kipi-plugins no longer use them and therefore dropped maintainership).
Remaining users of KIPI to my knowledge are:
@asturmlechner mentioned that Gwenview already uses purpose for some features and that it might fit the bill for replacing kipi-plugins.
To the best of my knowledge Gwenview doesn't use Purpose. I once looked into adding it since it would make sense.
Gwenview has a way to install the Kipi plugins that's been semi-broken for years so I doubt there are many or any users left. Spectacle shows them if already installed, but has no way to install them. Don't know about KPhotoAlbum. The last I checked, many of the Kipi plugins didn't actually work. And some are now redundant, e.g. Purpose can send via email too.
I'm in favor of retiring Kipi.
@ngraham: I wasn't aware that gwenview ships some KIPI plugins of its own, but here (Debian sid), the remaining KIPI export plugins are still listed in gwenview.
I'm not sure what you mean by "has no way to install them" - the general design of KIPI did not try to install anything at runtime. Plugins are usually installed like any other package via package manager and the KIPI-enabled programs use whatever plugins are available.
As for the status of KPhotoAlbum: I've just merged the purposeIntegration branch into git master today (actually, right now). So I guess any work on keeping KIPI alive any longer would be better directed at improving purpose...
I mean if you don't already have them installed via your package manager, Gwenview actually has a feature (which doesn't work) to allow you to do so by showing them in Discover. Making people figure out that extra functionality is available in uninstalled packages is not very discoverable or user-friendly, so GUI methods of discover and install such things are preferred. Unfortunately, as mentioned, Gwenview's doesn't work, and Spectacle has no such method.
As for the status of KPhotoAlbum: I've just merged the purposeIntegration branch into git master today (actually, right now). So I guess any work on keeping KIPI alive any longer would be better directed at improving purpose...
That's great news!
Did you check whether all the (relevant) features provided by the current set of KIPI Plugins are provided by Purpose plugins?
These plugins have no replacement in purpose:
I don't know whether all of these are in working shape, though. (Bugzilla is not much help, either: https://bugs.kde.org/buglist.cgi?component=general&product=kipiplugins&resolution=---)
I'm closing this issue for now because from my point of view the core issue seems to be sufficiently dealt with.