Since Tiki 21, some Tiki objects (wiki pages, blogs, etc.) can have maintainers, an update frequency and a freshness (i.e., low freshness means it has been long since it has been last updated). When an object becomes too old relative to its update frequency, Tiki will send emails to the owner reminding about the need to update it.
It'll be an extension to the Monitoring system, that notifies users upon certain changes in objects.
Let's take the example of a wiki page. When creating or editing a wiki page, on the Properties tab the user will be able to indicate an owner (user selector, possibly later groups) and the update frequency in days. The operating user will be the default owner.
A new console command, e.g.
objects:notify-maintainers, will sweep the objects and send emails to the owners telling them about the need to update.
A new Relation, e.g.
tiki.object.maintainer will be used to link users to objects. A new Attribute, e.g.
tiki.object.update_frequency, will store the object's update frequency in days. See: Object Attributes and Relations.