Ask HN: What sort of systemic risk to crypto is Paul Graham referring to?

There does not seem to be much exposition for the recent tweets from @paulg. Based on the tweets, however, we can assemble the following facts:

1) He's known his friend since at least 2012.

2) He (@paulg) didn't write that.

3) He is trustworthy.

4) He is convinced the "cryptocurrency economy" will shortly experience a "systemic risk."

How should we interpret these tweets from @paulg?