No, actually, the NetBSD dmesg won't help very much. At least, not here.
One thing you can try is a "verbose" boot - that produces lots of output, but you will see the last thing the kernel attempted to do (such as probe a specific device or device class).
- At the boot> prompt, enter the User Kernel Config tool with the "-c" option.
- At the first UKC> prompt, enter "verbose"
- At the second UKC> prompt, enter "quit"
Watch for the kernel output to stop... or to loop, and note the last thing it was doing ... or continues to do forever.
See the boot_config(8) and boot(8) man pages.