(Ouch, that was a painful couple pages on the thread...)
DiDA, thanks for the verbosity and guidance! Your hints were easily the most helpful I was able to find anywhere, so much that I felt the need to register and join this communicty as you finally landed both my iPhone6,1 and iPad4,1 running 8.1 squarely in the 'fixed and now running great' column. To clariffy my situation, my devices are clean restored, jailbroken and then restored with my iTunes backup... it's unfortunatly this last part of restoring my data that adds all the mess to the issue; any fresh restore/JB, I've not seen the icon problem with the latest Substrate and Cydia versions.
Running as root via PuTTY: uicache
...then rebooting, proved no results. Loading UICache Icon from the BigBoss repo didn't appear. Loading a free app from the AppStore, nada. Removing, reloading (Flex, iFile, MobileTerminal, iBlank, etc) yielded nothing. Renaming the mobile.installation plist did of course dump my icon display but no missing/new ones appeared so I reverted to my bak file.
For help anyone else with the issue persisting, here are the few extra steps I took:
-De-activated (not to be confused with 'disabled') any Substrate addons from their settings (Springtomize, mikoto, Eclipse 2, CleverPin, AppLocker, NoSlowAnimation, etc).
-Restarted with Substrate disabled (hold volume-up rocker during entire boot sequence)
-*Then* ran uicache, rebooted with substrate disabled again (this time it came up with everything displayed and I was able to re-initalize the iBlank bookmarks that were incorrectly listing as unknown/white target icons)
-Reboot normal (with Substrate enabled) and re-activate addon/tweaks from their Settings menus
-Reboot final time and all is well.
Thanks again!!