I'd like to see wildlife :
bears , wolves , sharks ,barracudas, etc.
wich attack you , so you can attack animals out of self-defense ,
new vehicles / objects for transport :
skateboard ? snowboard ? scooter ? ''lowrider'' bicycle ? weelchair ? hangglider? leonardo da vinci's helicopter? submarine ? jetski ?
weird folk:
a little town with a morbid secret ?, a yeti(bigfoot) wandering in the woods?, a psycho ?,
new locations :
castle/ruin? caves? ghosttown?
a wild river ?, with rapids and waterfalls, ( something new, because all water was on the same height in san andreas)
waves at the shore? maybe surfing would be possible