Hey I got it just before I read your reply!
Ended up just changing:
$this->bbcode_second_pass_code('', 'setenv bootargs console=${console},${baudrate} root=PARTUUID=${uuid} rw rootwait')
to:
$this->bbcode_second_pass_code('', 'setenv bootargs console=tty1 root=PARTUUID=${uuid} rw rootwait')
But I guess that will disable output on the serial console so I'll take your advice and just add 'console=tty1'.
Thanks very much for your help with this, much appreciated!