I think... about anybody who can run Crysis at Lowest settings should be able to run IV. I hope that IV is scaleable, meaning you can run it on a laptop with integrated graphics on lowest settings, as well as run it in full graphical glory on a nice gaming rig. I hope R* does that.
Although I have a over-a-year-old gaming rig with Intel Core 2 Duo, GeForce 8600 GT and 2GB RAM that should be able to run it, I hope I can run it on my MacBook too, even if it means San Andreas style graphics. Most people just want to play it anyway, even if it means losing the cool graphics.