Several recent games have had a zombie mode or DLC (whether it fits the setting or not), so one for the next GTA game is certainly possible.

My dream zompocalypse game would be something like a cross between a simulation and good fun, borrowing concepts from L4D (realistic city environments), Killing Floor (welding, or better still, using real objects to barricade doors), Fort Zombie (scrounging for supplies in the city) and GTA, with a dash of 28 Days Later (no place in the city is forever safe).
You have an objective to reach, but it's far away, and you may need a car (objectives and city are procedurally generated). The car is only 500m away, but you are holed up in a hotel room, and zombies are near your room. You have barricaded the doors, but it's just a matter of time before they break in. You can remove the barricades and escape via the front exit, or try to seek a way over the ledge outside your window. You decide to remove the barricade, and sneak past the zombies.
Downstairs, the roads seem clear. You quickly run, hoping the dash carries you fast enough to the car. Oh no. You hear padded footsteps behind you, and a bloodcurdling snarl behind. More snarls. You can't turn and look, because it will slow you down, and those zombies have proven to be able to run faster than you.
There is a petrol station in front, and it looks clear of zeds. You quickly run inside. The zombie is only 20m away from you. Desperate, you push a shelf against the door, blocking the zombie's smashing entrance (sorry, just had to) in the nick of time.
The zombies are now swarming in from all over the place. They hear you. You quickly find another way out - the roof. There is a shotgun on the floor. You pick it up, and realize it only has 7 shells left. Better than nothing. Quickly, you climb the ladder and out of the store through a crack in the roof. To be continued.
/orgasm
I was hoping Fort Zombie would be this sort of game when Kerberos first announced it, but then the reactions to it were...bad, and even the more positive ones didn't make it sound like the dream game I was hoping for. Alas.
-edit- Actually, looking at the LP thread posted above makes me more interested in the game. I'll watch more of it, hopefully it'll sway my decision.

My formula:
Gameplay from Killing Floor.
Atmosphere from Resident Evil series.
Levels like Left4Dead.
Diversity from Dead Rising.
Story from Dementium: The Ward.

Fort Zombie isn't actually that bad for a "not-AAA -title". Sure, it looks pretty old, zombies aren't that frightening and controls are a bit stiff, but overall, I like it.
But, you need to have the correct mindset when playing this. If you don't like zombies or survival games in general, then this game is not for you.
The base building and gathering survivors and essential goods for the final showdown is really fun! Running around the city while flocks of zombies chase you is pretty...well, fun :-)
And about the shooting and melee mechanics, well, it's an RPG. If you don't have the skills to fire a gun, then you'll probably miss. But if you do know how to handle a gun, then it's a different story altogether ;-)
All in all, the game costs a couple of bucks, and it's worth the money. Well, at least I think so :-)
Oh, and remember to put some points in stamina, since you'll be running a lot....

Now, come to think of it, is there any other good survival game (with or without zombies) out there? I know L4D and Killing Floor (which is a killer LAN game), but are there others? Maybe something that has gone under the radar?

There is obviously RE5 but the Resident Evil series seemed to have stopped being about zombies a long time ago. Nation Red is on sale on Steam this week and it's a mindless but fun shooter with co-op. If you have Fallout 3 then check out the Zombie Apocalypse mod.
Edit: I forgot Dead Space. Get it.

Well there is this game...
http://en.wikipedia.org/wiki/Survival_Crisis_Z
And it's actually pretty damn good too! Last time I played it was years ago, but it's fun. It gets a bit repetitive later, but then it's genuinely intense as you run around hunting for survivors, then when you find a room full of them, zombies suddenly break in and you have to hold the fort.
There are some indie games that are more "survival" in nature, but I can't really remember them atm. Then there's also Deus/Rob's Requiem here on GOG, but neither of them is a very friendly game.

Link!

Ah you know, these ones.

Bit too costly for me to take a gamble on, considering I have no idea if it'll be any good or a total waste of time, but it's interesting:
http://www.gamersgate.co.uk/DD-LOTD/land-of-the-dead-road-to-fiddler
A game based on George A. Romero's films. I've no idea if it's survival based or more of a first person shooter, but interesting nonetheless as mentioned. Didn't even know games had been made based on his films.