Pretty much impossible to get it working using Store-approved methods, probably out of the question even for homebrew. Cross app communication is handled through limited URI associations that are not built for apps to send notifications to a notification centre app in the background, and you don't get access to (toast) notifications of other apps.
Originally Posted by deadwrong03
At the very most, it will be hacky (probably using some sort of transfer other than URI, might be something silly like using EXIF data on an image) and will require apps to explicitly code for that notification centre. Not worth the effort, IMO.