Considering that continual content is a big part of GTA Online, I'd like to see comparable assets, such as ranches you could own and possibly have to cultivate in order to build your own "empire" of sorts.
I'd also like to see it have a different tone in terms of reality so that you could own fictional horses, such as the Four Horsemen horses from Undead Nightmare. Chrome horses? No lol, but I would be open to a unicorn.