I'm surprised to see this wasn't implemented from the outset, or that no one seems to have mentioned it, for a site that wants to be the one DPR users migrate to, but...
How about support DPR user names? I mean, people cannot replicate their DPR name if you can't even have a space in the user name. If your forum software won't support spaces in the actual userid, then how about implementing a displayed user name, or nickname, that allows a range of characters that mirrors what DPR allowed, so that people can maintain their moniker?
I had to change my user name on this forum, because it doesn't support the space character.