Money has always been part of the GTA series, but it's usually implemented as a secondary feature, a means to an end. In the original game you needed it to advance to the next map. GTA 3 saw it as a way to secure weapons and body armour.
Vice City, San Andreas, and VC Stories all played around with property and business ownership, Chinatown Wars had a limited drug economy. But it's in GTA 5 where we should see the most comprehensive use of money yet.
One of GTA 4's most limited aspects was how it handled your pursuit of the mighty dollar. Niko may well have been able to buy himself a suit, or a handy rocket launcher, but he could never use his enormous amount of capital to actually change anything bar the cosmetic.
It was a shame, because if there's one town that has the real estate and business potential for investment, it's New York stand-in Liberty City. Then again, Niko's story wasn't about founding and expanding an empire. For at least two of the characters in GTA 5, it definitely is.
Instead of being something you merely receive as a result of your nefarious deeds, here money itself is the goal. GTA 4 was finished and released before the disastrous financial crash of 2008. In 2013, the world is a different place, and Rockstar is using the poor economy as an influence on GTA 5. Half-finished skyscrapers adorn the Los Santos landscape, people are living under overpasses (in fairness, not too different from any era in actual LA), houses are being foreclosed. The bubble has burst, and now it's a case of no money, mo problems.
Which is why I wouldn't be surprised if money was a constant source of antagonism in the game, rather than any one distinct person or faction. In GTA 4, Niko is searching for Darko Brevic, a man who wronged him in his old country and turned Niko into the person he is today. CJ wanted to escape the oppressive clutches of the police, Vercetti was a gangster who wanted power over the mob he belonged to (and over Miami itself), and Claude wanted straight-up revenge over the girlfriend who tried to kill him.
Every character had a network of secondary players, who shared a common foe, or at least a common cause. Here, I imagine money will be both, your two other leads being your 'network.'
Everything we've seen so far seems to point to that being at least part of what the game is about. Although Trevor seems motivated mainly by personal 'issues', Franklin is a young man trying to make a name for himself. And then there's Michael, who has already 'won', but can't give up the excitement of it all.
So, 'greed is good' heists are in - with crews that have to be paid for, another intriguing point - and rampant commercialism is back. Tattoos can be inked, clothes can be bought, cars acquired and customised, along with (I presume) a whole host of other trinkets and toys. Again, GTA 4's equivalent customisation was far more sober, and grimy to boot - you essentially alternated between shell-suited eastern european immigrant or bank manager. Crucially, what you were wearing didn't matter for most of the game. Here, your appearance should have a lot more impact on your daily life in GTA 5, especially where Michael and Franklin - and their respective social circles - are concerned.
On a larger scale, you'll have plenty of ways to indulge your Gekko-esque bids for domination. Most obvious is property dealing, which appears to be so substantial as to have its own dedicated website. Then there's stock market dealing, arms trafficking, and businesses you can buy: cab ranks have been discussed, with a marina and helipad also mooted.
All of this should come together in order to allow you to put your own stamp on the city itself, as well as the characters you play as. The real question now is how does your new found net worth affect you and the world you inhabit? I'm not saying I want the whole game to be about paying the mortgage on your two-bedroom condo in Downtown, but hopefully it points to a different system than 'climb criminal ladder, kill the big bad guy.' In GTA 4 it made sense - Niko was looking for that 'special someone', was fresh off the boat and was an unconnected ant in among the looming skyscrapers of Liberty. Here, not so much.
In fact, Rockstar has already experimented with a concept that could work well with what GTA 5 is trying to achieve. GTA 2 had a gang reputation mechanic, wherein working for one of the game's seven factions would increase your standing with them, but reduce it with their enemies.
It was a clever idea, enabling players to choose their affiliation while also exploiting rivalries between the crime families they were working for. I'd like to see it return in some shape or form here, possibly to do with the so-called 'lawful' authorities investigating your actions.
None of this may transpire, of course. But it would also be more puzzling if some of it didn't, given the new format and Rockstar's promotion of money as one of the central themes of the game.