Hi thereI have encountered the same bug when starting the 3.12 kernel i built on my sunfire t2000.
On a sun blade 2500 (red) it boots.It shows the same switching to dummy console tty0 but then the xserver starts. On a sunfre v245 the 3.12.6 Kernel is booting, but i don't know if there is "switching to tty0" on the serial terminal.
I hope this helps. If you want i can try booting some kernels on my machines for testing. Greetings David