We would like to run some Java software (DB migrations) through the initdb mechanism, but it would have to connect to Postgres via TCP/IP, which isn't currently possible, since Postgres doesn't yet listen on TCP/IP sockets at that point.

Do you think it would be problematic if Postgres did listen on 127.0.0.1 during initdb? As I understand docker, this shouldn't expose the service to clients prematurely, but would allow initdb scripts to connect using TCP/IP.