[Sprint Galaxy S 5 Q&A, Help & Troubleshooting] finndo:
I guess this would be double posting, but I have a working phone and prefer to put what I did in a separate post, than to add it at the end of a bunch of troubles; The only thing not mentioned here but is above, I updated from 4.4 Alliance Rom to 5.0 OA6 stock via Odin, plus CF auto root via Odin, and ktTWRP (2.8.4.2) also via ODIN, as soon as the system came up to the welcome screen I rebooted to TWRP without doing anything and took a nandroid of all 7 partitions. And then updated to OF6 not knowing the new bootloader restrictions. The end problem was that OF6 did not boot. Below is a logging of what I did over the last 2 hours and the end result is that my OA6 nandroid is running with the OF6 bootloader? (not sure about this one), kernel? ( I think so), and modem. I am sure some of the more experienced guys around here would know. Personally I like to crack flash till I find something that works, then I might not flash again for 12-24 months, depending on if there were any bugs or not.

So here it is, I hope in the future someone somewhere is helped by this. If mods think this should be it's own post and chop out some of the useless parts to make it guide like, I approve of anyone else using this info and doing it.

wait times on boot up range from 10 minutes to 6 hours with no change. Any time something happens during boot it is always between 30 seconds and 12 minutes. Only while in recovery mode does ADB detect the device, with TWRP 70 it shows without permissions, with ktTWRP (42) it shows the device ID and allows access from adb.

flashed OF6 - Odin - AP

reboot - no audio - no boot

reboot - boot menu - factory reset

reboot - no audio - no boot

reboot - boot menu - wiped cache

reboot - no audio - no boot

flashed OD3 kernel - Odin - AP

reboot - audio - no boot

flashed cf auto root - Odin - AP

reboot for root install - straight back to Odin mode intentionally

flashed twrp 70 - Odin - AP

reboot - audio - no boot

reboot with vol+up - audio - no boot

reboot - twrp 70

flashed fusion 6.0 nightly 8/7/2015 - wiped cache and dalvik - reboot - got Fusion boot animation - no audio - yellow LED - after 8-9 minutes I got a blank screen - I pressed home and got "Unfortunately WFC Settings has been stopped" ok - "Unfortunately Phone has stopped" ok - blank screen - tap screen and capcitive buttons backlight comes on touch either bbutton, get vibration feedback, but nothing else, touch hardware buttons, screen goes off and on, but no other response. 30 seconds later Unfortunately phone has stopped, before I tap ok, I get a background image. Ambient light sensor appears to be able to dim screen brightness, no buttons give any visual effect, other than power button. No notification bar as of yet. 13-14 minutes after initial boot start up, the phone restarted itself.

reboot - loop? - Fusion boot animation - no audio - 4 minutes alter I got "fusion is starting" - lasted 25 seconds - then black screen with "Unfortunately, WFC Settings has stopped" ok - then phone - ok - then both again - ok, ok - blank black screen - 6 minutes later and several "unfortunately ... has stopped" I realized the screen had turned off. Turned it on, and there was a welcome screen with a crash screen on it, I went to type this and the screen went black, welcome screen did not come back, 10 seconds later - adb detected the device by name/ID an says unauthorized - system crashed - adb now shows all ??????? - unauthorized - long press power button brings up the reboot menu (has "settings" but when I press it, it just goes back to the blank black screen) - the only thing that worked from teh power menu was reboot (I would guess power off does too) even gives me the reboot screen with the spinning thing. during the reboot notification and before it actually restarts, ADB recognized the device again.

reboot - during boot up ADB goes to ???? unauthorized for 30-50 seconds, then shows correct system ID/name and unauthorized again - LED is off for the first time since flashing rom (did not even turn off when disconnecting from PC, connecting to laptop, disconnecting from laptop, plugging in to wall, disconnecting, plugging in to laptop...) - boot took 9 minutes 20 seconds - came up to android logo, then Fusion is Upgrading, shot through the apps r

eal quick, then everything stopped again...blank black screen, Amber LED back.

reboot - TWRP 70 - restore nandroid - system/data only OA6 stock - factory reset

reboot - waited 60 seconds before getting boot animation - waiting patiently to boot, ADB shows correct device name and unauthorized the entire time, no LED - waited 30 minutes, still on boot animation

reboot - TWRP 70 - factory reset - restore nandroid - boot/system/data OA6 stock

reboot - no audio - 40 seconds later - welcome preparing your device this may take 3-4 minutes came up - finalizing android upgrade after 30 seconds - update successful - LTE, setup wifi, EULA, software update screen, none found... tap and go.. skipped - add google and samsung. The Sprint filled my System up with crap... looks like it is working.

***UPDATE - 8/15/2015

I had some issues with system crashing again after the first reboot, but I waited on a blank black screen for about 16 minutes and everything loaded up. seemed to run fine, same issue next reboot... Instead of working on it, I flashed fusion ROM, never booted, I let it sit on the boot loader for 4.5 hours (fell asleep), then I flashed MOAR, I have not had any issues since. Checking a few other threads led me to believe I had lost IMEI, possibly the entire partition as I had all of the symptoms after a firmware update; however it is all there, or the restore of my OA6 nandroid put it back, not sure as I did not figure that out until much later on. Good thing I followed at least one smart rule... NANDROID before FLASH! good luck everyone.