I just tried both the 20000416 i386 snapshot (and also a more recent
bootfloppy image, yesterday-ish). With both snapshots, booting on a
Tyan Thunderbolt with an onboard 7896, but with no SCSI devices
attached, the boot process goes into an infinite loop after setting
biomask/netmask/ttymask and printing 'scsibus0: waiting 2 secs for
devices to settle'.  After that, I just get an infinite stream of
"Timedout SCB handled by another timeout" messages.

Anyone else seen this?  Is it a known problem?

At this moment I'm flat out of SCSI devices to hang off either SCSI
bus, or I'd try that.