I remember playing the leaked version of half life 2 and wishing I hadn't bothered.
Your ideas to stop people leaking the game are good, but how much time/money would devs be willing to spend to stop people playing an unfinished game? What ever systems they can come up with, the piracy release groups will only take a few days/weeks to crack it.
Another thought is that this maybe a purposeful leak, in order to garner column inches as well as get the game some free beta testing.








