Just out of curiosity, can (or does it already?) the BGE implement FXAA?

Here's a link to the Nvidia paper by Timothy Lottes. (pdf)
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By the time you're done reading this, most of you will disregaurd this statment, because you thought I was going to say "you'll waste x time of your life."

Hm... I must admit I have no idea if it is the case. Your best bet would be to go in the game section of blenderartist and ask them. Most of the developer and users are there.