Hello everyone!
Power supply: 5v 70A driving (up to/relay controlled) two dozen units, mostly Pi2 and Pi3 with a few 4s in the mix; with a spare 70A ready to go should the first ever take a dump. They're currently header-fed which doesn't do the job with USB devices being driven from the Pi, but the headers are temporary as a proof-of-concept run for the project.
bootsync/bootlocal would require updating core.gz (or rootfs) which would work out fine for some, but the goal here was to use pristine kernel/init files and just append our own GZ to the pxe/extlinux configuration to make it plug-n-play without having to keep an inventory of all of the custom cores, or the need for mydata, which in PXE isn't a preference (nor an option in most cases.) The trial running pxeboot.gz (our init which overwrites bootlocal, adds nfs-utils, numerous drivers and a few other necessities) seems to be working flawlessly, but I still felt it best to inquire.
Scenario: A fresh, untouched machine boots via PXE, isn't in the system yet with its own storage, so this appended core boots with the updated bootlocal/sync files allowing it to create its NFS/AoE storage remotely, have the default profile (setup, desktop, server, development, etc.) created which in turn, adds the PXE configuration file onto the TFTP server, calls into DNS/DHCP where a hostname and IP are assigned so the machine can be looked up without having to know much about it and a few minutes later, the box is ready to be SSH'ed into for profiling and use. We still have to perfect VNC/RPC for the different platforms, drivers, etc. so we're not done just yet.
SD Cards: Over the years, I've bought mostly MicroCenter SD cards for in-house and Samsung for client use for different applications ranging from CCTV cameras to the Pi, and found one of the biggest flaws isn't just manufacturing/dependability, but it runs the chance the pads on the SD (or the pins of the SD socket) have a potential of not making a great connection over time, especially in tablets (where the card isn't sealed well), cameras, my truck's stereo! and of course, the Pi. We've overcome this with a two stage fix which has done wonders: First, clean the contacts with Iso/rubbing alcohol to remove oxidation/debris, especially for those cards that get frequently man-handled... then a thin coating of EKG/Electrode conductive gel - insert the cards in/out a few times in the socket, wipe off any excess on the card, and it seems to make a clean, conductive seal between the pins and the card's pads. For devices which have already begun to oxidize on the socket pins, an electronics contact cleaner (burnishing tool) tends to revive them well.
Thanks to everyone for their input! Take care and stay safe!