Yes, I'm aware, and 10.0 was laughably code named Cheetah, but neither of those monikers ever made it into the wild (pun intended), so Apple could easily re-use them in public now without any mention of the heritage--I doubt more than 1% of Apple's market ever reads rumor sites, and only a fraction of those will remember the old code names.
I agree that Apple may not ever use Lion--for some reason it just sounds funny as a nickname for an OS, and my non-techie wife agrees, though neither of us are quite sure why. Too monolithic of an image, perhaps?
Would open the floodgates on bad Lion King puns, though, so it wouldn't be all bad.