Sounds like a plan, though I too wonder what they would look like. Also who is going to judge whether someone deserves a 'badge' and while applying this idea, do you take the forum history into account as well?
They're small, and they look like the event they are associated with. Secret Santa could have an elf one year, santa the next, a present the year after that, etc.
I've said it before, there is no "judge" who hands out microbadges. You participate in an event like Secret Santa or if we do something like the hat again, you get a badge. X-year member, you get the X-year badge. Win member of the year, you get that badge. There could be a handful of "band" badges that would be free that a user could select showing they really like a particular band/artist or album, but limited to one free badge per year.
I really don't want to discuss this further unless there is a decent chance of it happening. No use talking about "what if" scenarios of something that won't happen anyway.