So when the farming update comes out I think a great thing would be to raise livestock, but not just any livestock, it could be monsters. You could even rent or sell the monsters to do combat in the game for you, or even to ride on top of them to get around faster or have them carry stuff for you. Monsters could provide things like milk, eggs, wool, etc.
Personal twist (optional)
In order to get the monsters a new profession could be added where you gather eggs from nests like in Monster Hunter stories and hatch them, you could even sell them at the marketplace, it would give money a whole new value. Maybe you could even befriend existing ones with a tamer profession or even breed them.