I'm sure people with screenreaders also may wish to know what to call the person they are responding to.

In addition to having the name field actually filled with any sort of name, this supposes screenreader users want to do that. I'd never call you Estelle for example. To me, you're inabook because usernames have more value and are more useful for me and I never look at names, wherever they are. It would be easy to decide what's actually useful info if everybody was using the site the same way but we don't. If you add to that that nobody can force users to use the 'name' field in the way you intend it, I sincerely doubt names would be more useful than usernames for a majority of users.