Unfortunately, entrenched business and political interests have made encoding flags and emoticons a higher priority.
They've become part of the language and it would be culturally insensitive to give them a big "fuck you, us westerner's don't need your damn icons, either keep those to yourself and hence don't be able to inter-operate with everyone else or stop using them even though they've been a big part of your culture for 10+ years"
Unicode is supposed to be the central hub for all graphemes, but I would certainly like to see some argument that emoji are actually graphemes. For one thing it's quite bizarre that suddenly Unicode appears to be specifying colors as well as shapes, which is one bright line I'd be concerned about. (There may have been colors before but they would be much more exceptional, and I'm not aware of any.) Unicode was ambitious as the all-grapheme repository, it's simply a guaranteed failure if it tries to become the repository of all vaguely iconic/smilyish/little pictures in the world.
Encoding Mii's in Unicode, brilliant! Nintendo should really try to get a spot on the committee.