I think this could be a common pattern: selecting a page in a pages field and having the following fields react to (i. e. query) this selection.
An example: using a layout field to design an individualized project overview page. The projects are children of the current page and can be selected in a custom project block.
It would be great to be able to select an image from the selected project as thumbnail and not having to upload it again or search through the images of all projects.