Stock images: Sure. Would it hurt if they're available to people with proper permissions under /cms/assets/whatnot?
ETP pages/flat view: Just because content items are available under their natural URL doesn't mean they aren't *also* available in a list view from an admin page.
Placing content: Same thing, the content item could belong to the admin UI package at first, then when you're ready, you move it to the right place.
I might be wrong, and any solution that brings us closer to where we ultimately want to be is an improvement. I just want to make sure it's given due consideration.