After getting your negative attention with the oh-so controversial title i want to relieve you from your worries because this addition could just be a turn on or off feature.
We could have very personalized selections where each player could decide what parts of the game he/she wants to be more challenging - rarity, animal sight, movement speed, incline speed amount, animal fleeing time, need zones time and size, and so on... Of course not forgetting animal aggression and their "wind-up time."
(probably best kept to private lobbies or singleplayer)
Or more realistically an option to switch from default to harder difficulties or even an introductory easier difficulty where diamonds and rares dont spawn but animals are dumber. Now these more broader rules could be put into multiplayer and harvest screens.
Ideally we would have both, as does The Long Dark. Default options for difficulties as well as a customizable one.
As you might have concluded... this does not add any new content or help people get better trophies. Indeed, this addition would be made for more immersive and memorable hunting experience, since this is a hunting game after all...
Also add option for higher FOV while aiming down sights!