Sadly, if they put something like Crysis level requirements in order to run the game; I wouldn't be able to run it on my computer.
The very big thing that would definately keep me away would be if they put DRM, limited activations/installations, online verification; I didn't buy Bioshock because of this. This would be the one real thing that would definately keep me from buying F4.
Otherwise I'll probably purchase it since it is unlikely any of those things occur.