I'm not so worried about having an unlockable bootloader at this point, just a working G4, the potential for rooting is something that might matter to me (so I can install and use Xposed). So here's what I ended up doing:
- couldn't get any KDZ or TOT to install for whatever reasons
- grabbed that UpperCut utility (very cool) and it allowed LGUP to properly connect to the G4 and showed F500S20v as the current build/version (can't find any damned info on this build at all so I have no idea what actual build/version of Android it really is)
- tried to use LG Flash Tool to flash F500S20m which I have no idea is the actual build (meaning Lollipop or Marshmallow) and the flash tool fails to connect (even with UpperCut)
- went back to LGUP and was able to flash F500L11d and had success to the setup screen (then changed the language to US English of course) after which getting past the Google FRP was basically no effort at all really, F500L11d is Android 5.1 LMY47D - this ROM is for some U+ carrier or something, and this phone was sold by SK Telecom so now I'm wondering where to go from here
I have an SK ROM from Oct 2015 showing build/version V20c (LGF500SAT-00-V20c-SKT-KR-OCT-27-20150) and I'm considering installing it and seeing what happens. Sure I'll probably screw something up at some point and brick the damned thing but again I figure it's $35, it's not going to kill me (but yes I'll be somewhat pissed).
So at the moment it's working fine, cool to the touch but I don't do seriously CPU or GPU intensive stuff in daily life, if I can get a solid stock ROM on here and disable all the crap I don't want (even though I'll still have a lot of Korean language stuff all over the place) and maybe get it rooted so I can use Xposed I think I'll be ok with it.
So far so good...