What happens to Pokemon that were OU and they're not anymore due to lack of usage?

[Syberia]

You could always just list it on the UU page; something like "these pokemon have been deemed too powerful for the UU tier regardless of where their usage statistics place them." Doesn't even have to be technically called BL, unless the pokemon fall from OU.

I really think we're making too big of a deal out of something that's rather insignificant in the grand scheme of things.

 

[X-Act]

Unfortunately, only chaos is ultimately in charge of how the tiers look on the site, so only he would be able to make that note you desire on the UU page. This hopefully isn't a big deal, as you say.