> base64_encode(hash('sha384', $password, true))

> ...

> The above construction may invite theoretical concerns about entropy reduction (i.e. 72 characters of raw binary without any NUL bytes comes out to about 573 bits of possible entropy, but a SHA-384 hash outputs are clearly limited to 384 bits).

Given BCrypt hashes are a mere 184 bits, I don't see how this is a meaningful concern even in principle. If you're brute-forcing search spaces this big you're no longer looking to recover a password, but find a collision.