I think if you we're starting up a new forum, then you could have it anyway you wanted. My username is pretty obviously for the shop, and if I could, I'd have that user id and a personal user id, but that would just get confusing. Other people, have user id's that we're that before they became a trading name, ie frogger.
I think that the forum owner or moderator should know your given name, and it's your choice to give it to other people, but I know / discuss argue, am friends & enemies
with people across forums and I know who's who by their user names, as they can be more unique, as you can choose that user name. I mean, you're not going to have a username that is nasty about yourself unless you personally like it for some reason.