Scott,
Those are great questions. Systemic functional linguistics uses "existential" for sentences like "It is raining," pointing out that English doesn't seem to want to allow us to do this without a dummy subject. (Another way of saying it is that the verb "to be" seems to require a complement.) "Raining is" and "Early is" don't feel right. This gets confusing because we often use a dummy subject as subject placeholder when we extrapose. "It is easy to love you" can be rewritten as "To love you is easy," with "it" as placeholder. "To love you" is infinitive clause subject and "easy" is adjective functioning as complement.
I agree with your examples. They seem existential to me.
Visit ATEG's web site at http://ateg.org/
Visit ATEG's web site at http://ateg.org/