multiplayer for that reason is a great idea alone to program it in, however id personaly keep the heart of metal dogs as single player, you will eventually find the games multiplayer comes to a natural halt and its awful in those with no single player player option,very sad to see them disappear.
im glad its got a solid single player mode as i prefer playing on my own.

not quite exactly the same thing but have a look at Nyvanny, its absolutely barmy, involves cat like creatures and has a good MP battle it looks like.