I've been thinking about nirvana and buddhahood especially in zen and came to some interesting conclusions. Now a lot of zenists believe this, maybe all of them do, i don't know to many other zenists, so i don't know.
You ARE enlightened and in nirvana, you just don't know it. So the enlightenment in buddhism is really just realizing that you are enlightened.
Now it's time for my speculation. If we're already enlightened, and in nirvana, then wouldn't that mean that nirvana is not the end of the cycle of reincarnation(samsara)? Just some thoughts.