> With HTTPS used almost everywhere, using this QUERY method (when standardized) could prevent bookmarking specific “GET” URLs if the developers thoughtlessly replace GET everywhere with QUERY.

You're bothering about non-issues. Bookmarks support GET requests, not any other verb. Like it has always been, if you need to support bookmarks then you implement bookmarkeable URLs to be used with GET requests.

Also, your far-fetched example failed to account for the fact that nowadays POST requests are used to query.