Yeah, I agree that some sort of updater would be required. Bulk would make sense to me, as you may not want to listen for every block type, on every page, on every load.
I feel this is something which the standard user might not run into, but imagine needing to re-update every blog post every time you updated a widget or reconfigure a CPT setting. I’m excited for the blocks, because it finally offers a good chance for loading dynamic content within pages and posts, but until some method of updating presents itself I have a hard time seeing any value to custom blocks in large scale environments.