As for RDJ's announcement, I'm assuming it'll be something Iron Man related since he's the one making it.
We don't know that he is making the announcement - I got the impression that it was a Marvel announcement that he was hinting at.
I doubt RDJ, or any other cast/crew member, is kept up to date about ALL things concerning the MCU. Only stuff that involves them directly.
It's not as if Kevin Feige comes home after a long day of contract negotiations, calles RDJ and says: Yo Robby, check this shizzle, we just signed effing Cumberbatch for Dr Strange.
So yea, anything he knows about 8 days in advance, has to do with stuff he's directly involved with.