I would suggest making cargo saddles and carriages detachable rather than being a saddle of their own as this would add more depth to those carts especially if both of these carts could have their own storage capabilities. As well as fixing the glitch with the carriage kicking people off when going over rocks.
Another subject I would suggest is to change how breeding works as it is far too difficult to breed anything unless you live in the tundra with over 20 penguins. I would for one buff the penguin's insolation ability, and change the temperature ranges that the baby animals can survive and breed as it is strange to see wild animals running around in a biome that supposedly won't allow them to breed.
I do agree with the idea of having creatures change from harvesting different resources much like how they already have corpse and resource harvesting. Instead break resource into two categories, food, and materials. that way players don't have to constantly sort through all the unneeded items. Also giving the creatures the ability to be aggressive to certain targets like the sailors.
Finally, the rabbits are useless to have, but I would recommend them to have a sonar ability while on a players shoulder much like the parasaur. This may sound strange to give a rabbit, but it seems like a cool ability given the fact rabbits will turn to any strange noises they hear. This could be useful within pve or pvp as the rabbit can let you know when that damn snake is coming up to munch on the animal on is taming or it can help in pvp to detect players hiding within the shrubs. The whole balance to this detection is the rabbit is really weak and can be one shot.