As I read over this, my view on this is very closely mirroring LaC's so far, minus the swipes at Touhou and Vocaloid. While I'm very, very hesitant to open the tagtype expansion floodgates, if we can do so carefully then a new tagtype for memes, brands, and references to things like bands and songs and artworks is something I can put my support behind.
It'd need to be policed pretty carefully, though, and this is where 葉月's definition laid out earlier would be useful. We just would be applying it to the new type, not copyrights.
It's still a pretty complex idea, though, and I'm not sure the gain over just using blue tags is big enough. Worth discussing at least.