In the meantime, there are some good Firefox extensions that can be helpful: NextPlease, Hit-A-Hint (that one may not exist well with some other extensions). I believe there are several more that I haven't tried. Any one else had experience with them?
If anyone is interested, I found out a lot of the keyboard shortcuts for the text/HTML editor in Moodle by trial and error. General navigation around Moodle by keyboard alone is pretty difficult though. List of shortcuts is attached
However, your "trial and error" effort was not needed, since there is a Help with Editor shortcut keys icon readily available at the bottom left of the HTML editor window.
I have done some trials like Sarah too and as Martin said there are some conflicts and all defined shortcuts do not always work (not even all of those mentioned in this list) with all browsers. There might be some kind of standard keyboard shortcuts but I haven't seen such strandards. Attached some common settings found elsewhere for most browsers, editors and programs.
In theory it is possible to define any keyboard shortcuts for different editors.
Thank you for your list Sarah!