I definitely think they it should throw a player back on land for balance - I think most of us would be upset being tossed into one of the endless lava pools lol. Though for experienced players I don't think it would be much of an issue (Based on most of us *hopefully bringing Fire Resistance Potions into the nether) - it's just about finding that balance.
As an extension on it's initial attack, I think if it fails to grab a player the "Swipe" it makes should destroy blocks, knocking out the safety of the bridge or land the player was on. Assuming it missed the player, chances are that player would not be significantly effected as they would be out of the way (hopefully). It would serve to add that extra rush factor more than anything.
That really is an interesting idea, I would love to see something like this come to life in Minecraft. Definitely a +1 here
I wouldn't mind having us in the Nether. Just a question, would there be any warnings or things at will tell you one of these are near. Or will it just pop out at random and pull you into the deadly magma ocean?
I think a unique sound effect would be important for this one. Even if it were something subtle, like a Creeper has - to help it maintain the 'ambush predator' style.