frail rock
I will not claim to know much of anything about the game's code, but as a developer I feel like this wouldn't be a terribly challenging feature to add to the game.
I'd love to see some very rare hybrids that could spawn on maps where both of their parents also could be located. With the coywolf example, there are obviously no maps that currently exist with gray wolves/coyotes (though, I think several of the maps would be candidates for adding wolves to coyote maps or vice versa). It would be interesting to see these hybrids (Coywolves and other examples) have a very small change to spawn, signifying their rarity, but perhaps offering up some kind of reward to suggest their rarity (maybe 1.5x credits earned or something along those lines).
Other than having a small chance to spawn, I think they would follow more or less the same mechanics as their parents--same chance of bronze - diamond or great one status, similar color patterns, etc.
I cannot think of any other hybrids off the top of my head, but coywolves have always appealed to me and it would make my day to see them one day in theHunter.
bold locust
simple dock
hybrid silo