This thread got my attention and some of my votes. It really would be an interesting feature and I would empathize with the idea very much but there are some flaws (which probably many people already pointed out; I'm sorry, I didn't read through the thread thoroughly).
As an example; the chat would be the flooded of [360NOSPIN] or [0ZU] (bad examples, I know) clantags all over the #osu, #lobby or any #country channels.
As much as I like to see those clans growing into good, active and healthy clans and making people more competitive... some are immature and advertising in a spamming-fashion. Meaning, even after they got punished (silenced or whatever) they'll continue doing it. You may think 1 is not so bad... there are some billion people living on this planet and almost 3 million Osu! players, some sharing the same traits as the other. Multiply 1 by approx +1000 and handle the spam they'll cause.
I wouldn't be really happy if I were mod, or any user that likes to chat in #osu or #lobby or whichever channel they're in.
My recommendations would be that the player can choose if they either want the tags to be "On" or "Off" in the Options.
Um... also, is the original poster still active...?