The technical contact is the first point of contact for Customer Support. The TC is the person who can best initiate a decision if the app needs to be migrated based on the reason of the retraction.
In addition it could indeed be useful to send a message to everyone who downloaded that version. It would be even better to have a pop up in the modeler on startup and another one on deployment. We wil probably work on adding that option to our platform.
Thanks for your feedback,
Director Customer Support Mendix
Imho I think that ALL technical contacts should receive the notice no matter what the version is. Because for instance we are in the middle of a sprint to goto this new version (and thus have not yet a node on that version) we do not get a notice while it seriously impacts my sprint.