UFC monopolizing MMA would be nothing but great IMO and people who dont agree just take a look at all the major sports in the US. Those sports wouldnt be half as big as they are today if they weren't monopolized.
IMO strikeforce are the last of the competition for UFC, if they dont make it big then i dont think anyone will, if Strikeforce fails UFC will have full control of MMA in the states and no one will be able challenge them again.
However, this may sound stupid, but i think there is only one company in the US that could challenge the UFC and thats the WWE and theres little rumours going about that they mite do. They have way more money than the UFC and have a ton more of experience in the Entertainment business(which MMA is) too.