Macbook pro 10.8.3 Safe boot hangs

Question

Retina MacBook Pro Mid 2012 running 10.8.3 with latest SMC update.
My system will not complete a "safe mode" boot, it hangs with the progres bar at about 1/4 of the way. I am trying safe boot to be able to run the system while all extra drivers etc are disabled for diagnostic purposes.
Things already tested:
From Recovery Drive: Disk utility has been used to repair the disc and reset permissions.
From the Recovery Drive, start terminal and run "fsck_hfs -f  /dev/disk0s2", completes correctly
I tried a save boot with verbose mode on. (In terminal before reboot, execute "sudo nvram boot-args="-v -x" )
The boot process shows it passes the fsck_hfs (no surprise), then it shows:
IOThunderboltSwitch(0x0)::listenerCallback - Thunderbolt HPD packet for route = 0x0 port = 12 unplus=0
AppleUSBMultitouchDriver::checkStatus - received Status Packet, Payload 2: device was reinitialized
And there is hangs.
So it looks like whatever comes after the Multitouch Driver initialization is what is causing the hang.
Any suggestions about this?
Is this a hardware problem or a software one?

Answer 1

Having the same problem, with a 2014 MBP running Mavericks 10.9.5, no peripherals connected.
Took it to Genius Bar today, where they reinstalled the OS, and after taking the afternoon to get it up and running again, I'm again having the boot problem. It hangs at exactly the same place, right after the AppleUSBMultitouchDriver::checkStatus message. Only difference is that before today's visit it wouldn't boot into Recovery mode -- it'd only boot to Single-User -- and today it will. It won't boot into normal or Safe mode.
This is a nearly-brand-new MBP, so hardware failure (while certainly possible) seems a bit improbable. Other points against hardware failure:
booting into diagnostics mode, the system reports all is OK
fsck is not reporting any errors
when I boot into Single-User mode I can still read files on my hard drive (e.g., system logs in /var/log, my user files)
it fails to boot even with no peripherals connected
Can anybody point me to a detailed list of the events that should occur in a successful boot? Specifically, I want to know what should happen after the MultitouchDriver event mentioned above, since (one would think) that would narrow down the list of places to look and questions to ask. The standard procedural info ("just reinstall the OS") isn't reassuring.
Oh, and I tried to post this as a separate question -- after all, my version isn't 10.8.3 as this thread suggests -- but the browser in Recovery mode (Safari 7.0.6) won't let me post a new question. (On the main page for this community, the search box's "Submit my question to the community" does nothing when clicked, and often neither do any of the links that come up in search results.)