Updates don’t currently have a way to ensure that user installed packages have their configurations updated appropriately, so user installed packages may break on update. Additionally, as a sibling comment pointed out, official images don’t include user packages, so you’d either need a scalable way to build custom images or the updater would need to be smart enough to reinstall packages after update.

It would still be nice to have an official automatic update feature that is opt-in for stock systems.