Please correct me if I'm wrong, but doesn't the changed partition structure mean that even if we had an unlocked bootloader and CWM installed, we won't be able to flash Stock GB/CM7/CM9/CM10 roms on a device that has had the LG ICS update?
It will take something that will rewrite the partition sizes like nvflash/smartflash/KDZ updater and that will also wipe everything on the internal memory including the internal SD card. I'm guessing CM9/CM10 is just going to use the old partition layout so that they can just be flashed over CM7 using CWM, so it's not going to be easy switching between stock based and CM based roms anymore.
Things are certainly going to get more interesting for the guys cooking up the roms again, and "dicking around" with the phone is going to be a little more complicated.
Actually, on linux you can change the partition table around quite a bit without data loss. I can't seem to find the partition table layout (30 pages..) but if I recall correctly the 'sd card' partition was the same size, so at least that one will be intact (and could in theory be used to backup /data, not sure if OEMs do that sort of stuff) It's also possible to move/resize partions without data loss, but this is of course a bit tricky. However, with a bit of time and guaranteed power (adapter connected) it's pretty safe.
Man, I which I had the time to contribute to this, my linux skills are OK, my coding skills are close to zero but still. So not much remains but wishing the guys working on this godspeed, and thanks a heap!