Sin: Would unified theming (something like qtcurve) belong here? How about another high-level service, a web browser element (webkit) that can be used from any application?
Elektrolott: How about using Akonadi?
Akonadi - The PIM Storage Service Mission Statement We intend to design an extensible cross-desktop storage service for PIM data and meta data providing concurrent read, write, and query access. It will provide unique desktop wide object identification and retrieval.