GtkRecentManager is incorrectly conceived IMO
I don't believe the typical GNOME user is going to be working with such a small set of files that having a shared set of 'recent files' across all their apps makes much sense.
Specifically in my case, I am opening a lot of files in Geany, and then finding my recent files in gedit (which I use for standalone .txt files) totally useless.
I realise I can deal with this specifically by asking Geany not to populate GtkRecentManager, or ask gedit to implement it to only read out its own files from GtkRecentManager, but IMO the whole concept of GtkRecentManager needs to be revised because this is a generalized problem that should be solved at the layer of GtkRecentManager.
There should IMO be a GNOME config option to specify whether apps have their own recent files menu, and GtkRecentManager should respect that. Apps should also be able to override that on an app-by-app basis.
GtkRecentManager would have to take on the responsibility of filtering down the recent files based on context and configuration. As a side note, if doing this, GtkRecentManager might as well also take responsibility for handling its existing private feature within its own API rather than asking users of the API to respect this.
I realize this would all require a major redesign of the GtkRecentManager API, but I think its important and therefore worth doing at a point where this is feasible.