I finally caved and decided to jailbreak my iPhone 6. Been a few hours now and I've installed a whole bunch of tweaks from the approved iOS 8 compatible tweak list and managed to modify the Gunnii theme to work well enough on iOS 8. No unexpected crashes, no boot loops, no crazy battery drain. Glad I waited!
iPhone 6 - iOS 8.1
Theme: Gunnii (plus personal mods)