I've been planning on redoing / extending the end sequence of the film to be more akin to the original games [remember the bunny head on a spike, anyone?]
What I'm planning atm is to have the Elevator surface only to reveal that a few zombies are roaming around on the surface.
After that I'm planning a short montage of destruction culling footage form about 5 different movies...finally to reveal a title card saying something like
"Doom2 : Hell on earth.
Coming soon."
Here's a quick mockup I did as a test for a few things..It's not really representative of the edit but this shot may wind up in the montage - it's form 'the reaping'...

As long as I have time to play around in the next few days, more test shots will follow.