It seems like a good policy if people abide by all the rules.
I'm all for Disney becoming more pet friendly, but I have to admit, I don't think I'd be keen on staying in a room where dogs have been staying. I have enough phobias of hotel beds as it is, without knowing a dog has been sleeping in them!
The only other draw back I would have is that Disney keeps the grounds pristine and there are always those dog owners that don't follow the rules, or clean up after their animals. Disney would have to implement and enforce some pretty strict guidelines.