Okay so I've had similar ideas before but they end up too complex! However, it did get a lot of interest so I'd hate for the idea to die XD
There would be three "main" character types.

Prey ~ They aren't personal characters, they are purely for hunts etc, they WILL die fairly soon into roleplay.
Mortals ~ These will be the main bulk of the game, they can die, however it's not definite. They're for realism and thrill. Don't get moody though if they do die, deaths will be decided by the roleplay managers or the owners. However, roleplay by the owners will affect their mortality.
Immortals - Technically they're not immortal, however their death can only be decided by the player, or if the player abuses the rules.

Typically the roleplayers should only have 1/2 immortals, then some mortals and the prey can be played by anyone. However, only managers can put them into the game - To prevent too much food.

There will be territory, un-claimable land and various other areas. Which will be written down and these are the only areas roleplay can take place in. However, you may request for more to be added!
Territory will typically be the most wanted places, however it will be fought for as it is most valuable. Un-claimable land is typically much harsher to survive in, but no one can stop you entering and using it's resources.
Other areas are undecided but some ideas are urbanised areas, sea and is open to suggestion.

So various species could be included, wild cats, domesticated, dogs, wolves, horse etc. However it would have to make sense in the ecosystem. Nothing like a fire breathing tiger-wolf.

A lot is still undecided to please comment your ideas. Or if you're interested in joining ^-^