Anyone who has played Skyrim will know what I'm talking about. After you beat fixed, scripted, official, missions...you have the option of doing radiant missions. These quests are literally "never-ending"...you initiate a generic dialogue sequence and then the game handles the rest.
Sure, it's not as detailed as the main missions but they add personality to the post-game.
For instance, in Skyrim you can get "monster hunter" radiant quests. You talk to an NPC, she says "A citizen of _____ needs our help!" and then the quest journal tells you there is a Sabre Cat near Solitude that you need to kill.
Now let's apply this to GTA.
For example, the bounty missions from Maude. There are only 4 of them...I was very disappointed by this.
A "radiant quest" system would be easy to implement. You go to Maude, you get a generic dialogue and text "Hey Trevor, there's one asshole you need to bring in"
Then, on your phone, you get a randomy generated text "Mr. Derp near Fort Zancudo" or "Nail this scumbag by Grapeseed!"
The game then spawns a bounty and a bunch of guards in any area of the countryside, you go and kill them. Simple. In open world games this is easy to implement. There is so much detail, so many sights, so many places...it's a shame that so many of them have no purpose.
The text works like this: once the game spawns a cluster of enemies in an area, the area-detection then programs a text-message on the fly. The game CAN recognize which borough you are in. When you drive around, you can see it in the bottom right corner where the vehicle name is displayed. This has been a feature in every GTA.
If there is anyone who is unfamiliar with Radiant Quests, read this: http://elderscrolls..../Radiant_Quests
You can, of course, apply this to other scenarios. Let's say Franklin being a vehicle enthusiast has "car repo" missions like Brucie would issue to Niko in GTAIV.
A random vehicle spawns with hostile NPCs around it. Frank gets a text saying "Yo nigga, get me dis Entity XF that got boosted by some Vagos niggaz in Vinewood hills"
You go there, kill the hostile Vago NPCs, and then drive the car to a predetermined garage.
It adds to the character, immersion, and gives you something to do once you exhaust the limited side quests. 4 bounties, 4 bounties? Seriously?!