Okay, the first draft of new key names is more or less ready for inspection. A few notes:
I've tried to stay close to the JS filenames where possible, but in some cases I've opted to go with something that would make more sense to a translator, who shouldn't really be concerned what JS files are called.
I've broken some locations up into smaller chunks in some cases; in others, I've used prefixes to gather related chunks together, so that translators will have an easier time navigating the YML file. In many such cases there's a judgment call to be made, and I've got with what strikes me as convenient.
There's still room for discussion on a lot of the names, especially in regards to the granularity of the chunks.
As mentioned earlier, a couple of links (one log_in and one sign_up) need to be merged with the text strings that precede them to create prompts. I'll have a look at the code as I get started on editing, and I can't manage the changes, I'll call for help.
All in all, I think this is turning out pretty well...