New permissions shouldn't be taken lightly. One day you'll install an extension that access only on a specific site, and the next day it's requesting access to all your bookmarks, location data, history etc. If you make it into a next next next dialogue box you're implementing an easily abused dark pattern.

A better approach would be to allow extension upgrades, irrespective of permissions. If a user chooses to deny permissions the extension should still work on the latest version.