Until now the next-gen/PC GTA 5 didn't really interest me all that much but if it includes this first person mod I will be in there like a shot.
This FPS script is the work of XBLToothPik (via CVG) and uses a modded Xbox 360 to hack the game's perspective. Obviously that's out of bounds for most people but an interesting proposition for when the PC version arrives.
And here's a bonus video showing what sort of stuff a hacked Xbox 360 can do with GTA 5. Terrorize lampposts mainly.