Hmm.. two things...

1. If the client is sending it's initial SETTINGS as the value of the HTTP/1 header, why would it need to send yet another initial SETTINGS frame once the server responds? It's certainly allowed to, yes, but why MUST it?

2. Empty header would just mean default settings, correct? It would be the equivalent of the client sending it's initial required SETTINGS frame with no payload (which is currently allowed). So that should not be a problem.