Hi Guys,
I have been mildly entertained by today's earlier discussion/debate. I don't think any of us disagree that WordFence can do what it has been programmed to, but that some of us want a little more fine tuning on what it can do (myself included, as I made two optional implementation suggestions above that would satisfy what has been suggested).
For restricting usernames, definitely check out the plugin that @sgpark suggested: https://wordpress.org/plugins/restrict-usernames/ as it will have additional options that go above and beyond what I'd recommend WordFence get involved in. (That is unless the WordFence developers want to go that route.)
For blanket blocking certain usernames, I didn't find anything too specific online, so I wrote up a simple plugin script. All the variables (i.e. blocked usernames) are in the code itself, so if you know a little bit of php, it should be very easy to modify to your liking. Also, if any more savvy programmers want to turn this into an official plugin, be my guest.
I don't know how involved WordPress runs when trying to log in users, but this plugin is pretty light weight in that there are no WP settings or really anything added to the DB to cause bloat. One should use WP's internal plugin editor if they want to make changes (or FTP + your preferred code editor).
Note: My code doesn't "ban" bad usernames IPs or anything, it just sets up a brick wall that stops the WP Login process for the usernames in its list. Also, its priority is set to run between WP's initial checks and WordFence so you won't get WordFence generated emails notifying you when this plugin blocks a login attempt from one of the banned usernames.
For those of you who are interested, enjoy. :)
~Cam