As of today we already have the maximum of five migration targets, one of which is meta (this site).
I've actually been watching migration statistics for a while, and four of those five correspond to our most common migration targets.
One of them, however, does not, and hasn't had a post migrated in a very long time, as far as I can recall. That target is, of course, meta.
I would cautiously support replacing that with the next most commonly used migration target, Webmasters, as we get quite a few questions which may be better suited there, far more than are actually migrated since it isn't on the list.
I've since been informed that meta is a mandatory migration target and can't be replaced. Oh well, it was a thought.