It actually looks like it might happen for KDE4, but will be quite some time. I just found this on the KDE PIM mailing list:
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kitchensync uses opensync 0.22 (the latest stable version), and the kdepim-sync plugin of that version uses the KDE3 libraries. So you probably can't sync with that version against KDE4 as KDE4 uses a different default location of the PIM data (~/.kde4 instead ~/.kde)
I didn't try if there is a workaround to that problem.
Currently there is no kdepim-sync plugin which links against the new KDE4 libraries, and there is no work put into the already old version 0.22 of opensync. Instead, there is heavy work going on for the next stable release 0.40.
However, work has been started on a new KDE4-PIM opensync plugin which uses the new Akonadi infrastructure, so at some point in time after the release of opensync 0.40 there will be a working KDE-PIM sync again.
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According to the roadmap they might get done in the next 6 months. Too late for me, but...
Roadmap – OpenSync