Comment by pclmulqdq

Blake2 also uses a very SHA2-like construction (a HAIFA construction, which is based on Merkle-Damgard). I believe this was the main reason SHA3 was chosen to be something completely different (a sponge construction). If SHA2 was found to be insecure, Blake2 would be at more risk of also being broken than Keccak.

Speculatively, if SHA2 is broken without breaking Merkle-Damgard hashes in general, Blake2/3 could well become SHA4.