They did that with ARMA II - or something like it. It warned that "illegal copies may degrade". I personally pirated ARMA II a couple of times, and the results were pretty hilarious. Look up some videos of it.
Basically you start your "basic training" in the game, and in the middle of it the instructors turn into enemies and will kill you. Mission over. You can't complete just about any mission - friendlies turn into enemies, random enemies spawn and shoot at you, vehicles don't operate correctly, etc...
I think it's a neat idea and is funny to watch - but quite honestly when I played those cracked versions I didn't realize that's what was happening...I just thought the game was fucking awful. Therefore, I never really gave it another chance even though I'd heard good things about it. Now, 2 years later, I finally bought it and the expansion and play DayZ quite a bit and love it. But yeah, I probably would have bought it 2+ years ago if I'd known what it was actually like, rather than how the "degraded" version played.