We understand your concern and use-case regarding the new function UpdateKeyByQuery(). But as of now, we don't have any plan to release this functionality. I am forwarding your request to our production team, if we get more request then definitely, will take this on priority and release in our future updates.
As of now, you can use multiple functions to update the document like first fetch the list of documents using query method and then update specific key using addOrUpdateKeys method of Storage service.
Let me know if you need further help from our side.
We will be happy to help you!