Category as tag
Treating every category as tag makes it easier to integrate with other content in the real web 3.0.
Data in mediawiki format has only one type of tagging universally supported: the mediawiki category. Since users adopt target categories when they copy wiki pages or fork wikis, having all such categories come from a common pool of tags that are widely recognized in the language and idiom used. Without deliberate adoption, it's even more important, since pages with the origin categories could not be easily placed into the target category scheme. And, lack of support for any open tag service has made it difficult to ensure that wikis are easily linked from blogs. Not supporting this yet is one of many mediawiki gronks.