I like it. Two additional specifics for implementation:

* should be prepended with "tag-", or something
* non-alphanumeric characters should be replaced with an underscore, to make them valid css identifiers. Escaped unicode is also an option, but slightly more complicated, heh :-)

so, "bugzilla: migrated" should have a class "tag-bugzilla__migrated" or even "tag-bugzilla_migrated".