I think it would be very simple and add a lot of fun/replayability of you could put together a download with:
1 - an additional difficulty level. Post human warrior is fun but I still feel that I am overpowered and survive way too often when I do dumb stuff. Delta from crysis1 required exact precision, patience, and really pushes your abilities even with quicksave. posthuman is too easy! give us an equivalent to delta mode!
2 - "port" the x-box/playstation achievements over for us pc players! As much as I hate the concept of a port I do find it fun to have extra little challenges to find above and beyond murdering everything that moves.
I think this would be easy and awesome and add alot to an already great game! anyone else agree?