Hi Matt,
I would not recommend you forking the code as that will make it very difficult to upgrade.
I don't think it would be difficult to add a web.config option to hide the user id if using email for login, but it still needs to be maintained in the db and must be unique per user, so it will require adding a little logic when it is hidden to populate it and ensure it is unique. Could just use the part of the email address before the @ sign and if a username exists with that then just append a number to it to make it unique.
However, the member list and ProfileView.aspx also displays it, the idea being we don't want to expose email addresses there and the userid gives something pseudo anonymous to list members by. So we would need to figure out what we do want to show there if we hide userid, maybe full name.
I will make a note of this on my list, I'm working on other things right now but if you want me to make this a priority a small sponsorship or donation would probably do the trick.
Best,
Joe