6. Phone Customisation
When it comes to open world games, we all want to customise everything. We want our own car, our own set of clothes, our own hair cut. In the Saints Row series, you can even choose what voice your character has. And ever since GTA went 3D, gamers have wanted to fully customise their own character, right down to gender and ethnicity. But it seems Rockstar are never going to go down that route, but maybe they would let you customise your smartphone. And not just a new screensaver like in GTA IV, but the option to pretty much have your own phone. There could be a new category of store that lets you buy new models; perhaps you have to upgrade in order to go further in the story (or to get the hacking software I mentioned earlier), or maybe this is where you can buy new games for your phone. Something like this wouldnt be that important to the overall gameplay, but it would just add to the novelty and 'Wow, GTA V can do this' feeling.
5. QR Scanner
If you havent heard of these, QR codes are barcode-type boxes that contain codes that, when scanned with a phone, send you to a particular website. Several games have included these hidden within levels, including Deus Ex: Human Revolution, which had hidden codes that sent you to a real-world website of the fictional company Sarif Industries when scanned with a real-world phone. But why not have this system with the in-game phone? There could be hidden QR codes throughout the game that, when scanned, sent you to hidden websites. They could be used as a new type of collectible instead of the hidden packages or shooting pigeons, or scanning QR codes could be the new way of accessing cheat codes in GTA V, instead of calling numbers like you did in GTA IV.