Indeed, adding "console=tty0 console=ttyS1,115200" to the append line in extlinux.conf, now the serial connection works.
But initial-setup, even if the answers appears in the serial interface, doesn't work: in reality there is a login screen.
Here you can find a screencast to better understand: https://alciregi.fedorapeople.org/webm/rpi3serial.webm
Using the hdmi monitor and the keyboard, initial setup works.

Ciao

2017-09-26 19:48 GMT+02:00 Peter Robinson <pbrobinson@gmail.com>:
On Tue, Sep 26, 2017 at 6:03 PM, Alessio Ciregia <alciregi@gmail.com> wrote:
> Someone has tested the latest RC of the Minimal image on the RPi3 using the
> serial console?
> Maybe I'm wrong, but it doesn't work as in previous composes was. It stops
> printing on the serial console as soon as the kernel is loaded. The append
> line in the extlinux.conf file seems ok.

There was a change/regression where you need to specify ttyS1 for the
console, not S0, I believe it should work fine for that, I think I
know what the issue is but I'm traveling this week in endless meetings
so I've not had time to verify my theory as to why that is

> Tomorrow I will try again. In the meanwhile could someone confirm that it
> works?
>
> Thanks
> A.
>
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