I was thinking the same last night. My thoughts are that they'd just drop the OS firmware over top of Android leaving the boot loader in place; same as flashing Android proper over device original Samsungandroid. That's what I'm hoping anyhow.
I'd like to see a dualboot option too personally though if it's one or the other, Ubuntu is a pretty good sell.
I'd also suggest a full phone backup including your CM backups. Wugs makes it easy.
Keep Up with TechRepublic