I think it is a good question.
When there is yesterday morning and tomorrow morning, why have an exception for this morning (which means today's morning)?
Yes, idiom, but i actually do like.
No, as of can mean both - 1) as of today, only three survivors have been found.
- as of today, all passengers must check their luggage before boarding the plane.
Today had been the worst day of my life.
Seems awkward, as today is not understood to mean on this day (the original meaning).
In narrative, an event that is happened in the past is narrated.
Today means the current day, so if you're asking what day of the week it is, it can only be in present tense, since it's still that day for the whole 24 hours.
In other contexts, it's okay to say,.
The apostrophe indicates possession.
Without an apostrophe you are indicating plurality.
Since the point you are trying to convey is that the assumption you made yesterday is no longer.