Being that, at least for now, we have to live with 30ish GET requests, I would like to let my users know when the editor (and page) is available for them to use. Is there some client-side event that fires when the last of the initial GET requests has been issued? I am hoping I can use that event to update the UI so the user knows they can proceed.

With a full implementation of RTE, the visual clue [that it is ready] is the user can see RTE buttons all appear one-by-one. But when configured as an image selector or file selector, there is no such clue, and the page seems unresponsive until all the GET requests have completed. 

Note: My client-side config is very close to your image selector demo page. 

Thanks.