Just checked out -current and built a new kernel...

[yadda yadda]
pci1 at mainbus0 bus 1
pci1: i/o enabled, memory enabled
ofb0 at pci1 dev 11 function 0: Apple Computer product 0x0003
ofb0: 640 x 480, 8bpp
wsdisplay0 at ofb0
wsdisplay0: screen 0 added (std, vt100 emulation)
panic: kernel diagnostic assertion "scr != NULL" failed: file "../../../../dev/wscons/wsdisplay.c", line 1451

Stopped in  at  0x223058:       lwz r0, r1, 0x14,
db> 

This is a 7300/200, which has:

FF83DCD0: /chaos@F0000000
FF83F658:   /control@B

for a flamebuffer.

It's also noting that this device can do at least 1280x1024 (which is
what we use under MacOS).