Interesting, I didn't know about that. The cat-and-mouse hacking race on the 360 was fierce stuff. Interesting that Microsoft had such success warding off unsigned code execution but left a massive hole in the DVD drive that took ages to close down (somewhat).
3.0.1 completely changed all the keys and all sysmodules, etc, were changed/recompiled with new the new keys.
3.0.1 is, effectively, an entirely new FW.
Yes, but PSP (Pro CFW, M33), PS3, original Xbox (Avalanche), Xbox 360 (DashLaunch) and even the 3DS in the form of a bootloader have custom firmwares. You can update to them and still access homebrew and games. So hack your 3.0.0 device and wait for someone to create update packages without certain security features to bog it down. This has happened plenty of times in the past.
Well, yes, this is even on the PS4 on 1.76 (TLOU bundle) where the system was cracked wide open but later updates patched it closed entirely. Same has happened here.