libkipi was, until recently, a dependency of gwenview and spectacle (and maybe some other applications in the Arch repos). Those dependencies are no longer necessary.
Here’s the commit that removed libkipi as a dependency of gwenview (notice line #13), and here’s the commit that removed it as a dependency of spectacle (line #10).
The package was kept available by moving it to the AUR because it is still required by 2 AUR packages (spectacle-light and kipi-plugins, both of which require either libkipi or libkipi-git).