I'd very much like it if MoinMoin allowed Macro developers to not only hook code into when a macro is displayed (as it is currently), but also into when the Macro is entered onto the page, or changed in a subsequent edit/delete cycle.
This would allow Macros to ack as 'triggers', so that they could (for example) write information in the Macro to the data directory, thereby enabling people to use it for other purposes.
My immediate application is that I'd like to write a Macro called PageProperty that takes two arguments; a property name and a property value, both of which can be either plain text, or a WikiName. By providing a trigger when someone edits it, I can collect information about pages that contain PageProperty Macros, which can be displayed by other macros.
For earlier thoughts about this, see this blog entry.