KDE's Project Silk

I think you have it backwards. Akonadi has had very limited usage within
kde, gradually increasing as apps are ported to use it. In other words, the
ideas were implemented using tools that worked at the time. Proof of concept
type thing. As it becomes more useful, more integrated, the availability of
suitable backend libraries hopefully improves at the same time. But the
necessity of getting something out there for people to bang on forces bad
choices.

Really, all this episode shows is that for serious desktop work, developers
run into serious limits and sometimes walls that gives them the choice of
writing from scratch or using something inappropriate. In this instance due
to the lack of a lightweight full featured data/storage/retrieval engine.

Derek