Re: Block 4 is not completely dead yet
There are five block 4s left that could fly again. One new one launching TESS and landing on the 16th, three of the other four have missions planned (first is CRS-12 on the 2nd). Boosters for TESS and CRS-12 are expected to land. I do not know about the others.
There are two and a bit block 5s. First block 5 launch is no earlier than the 24th. There are no Falcon heavy centre cores, but one is scheduled to launch no earlier than 13th of June.
SpaceX probably run out of block 4s some time in June.
We have plenty of time to think of an insane payload for BFR's demo mission. My first thought was a fully fuelled Exploration Upper Stage (crew vehicle for SLS) but SpaceX are not set up to load liquid hydrogen and EUS probably won't be ready.
Biting the hand that feeds IT
