So far, we know of sharks and deer as a sure bet for GTA V, but it's odd that the latest reveal talks of some Wilderness, but shows instead, something more akin to a field that would be found just outside the City's confines. Nothing resembling a forest, but that would be nice, as there were portions of the map in GTA's classic San An that did feature a lot of hills and trees, and when planes crashed into such things, whether AI driven, or under your control, provided some funny crash moments.
Hoping that with the new revisions to GTA's LS, that some of those funny programmed by accident moments still exist, Two key examples are cars crashing at insane speeds in SA and bursting into flame, and planes flying too low and hitting any number of obsticles before crashing to the ground in fireball wreckage! I think the game's AI will be more spotless then before so those moments would likely be more thought out but we'll see. Often it occurs from glitches that are part and parcel of a huge programmed game, hard to iron them all out
For nature, in RDR, the main thing I liked about it was birds and rabbits or other small animals showed up all over the countryside providing for a much more animated vastness then could be had in the past with GTAs' where only peds conversing, or milling about, or key sequences provided much action across the map.