Update: GTA V on the Xbox One, Playstation 4 and PC has now been officially announced!
If you are looking for a "GTA 5 on PS4 and Xbox One" announcement any time soon then you're out of luck. It's not happening.

Speaking recently to MCVUK, Strauss Zelnick, CEO of Rockstar Games parent company Take-Two, had this to say:
The installed base of current generation consoles is estimated to be in excess of 120 million, and most of those consumers have been waiting for Grand Theft Auto V for years. Therefore, we expect there to be enormous consumer demand for Grand Theft Auto V regardless of when the next-generation consoles are released.
Sounds like he doesn't feel any need to start looking at releasing GTA V on the PS4 and X1 in the near future... Also weighing in on the next-gen issue is Rockstar Games co-founder, Dan Houser himself. Speaking to IGN recently, Houser had this to say:
We don't feel there are that many limitations in the Xbox 360. We feel we can do some very impressive stuff and do it for a large audience.