EDIT: People are still tracking this, so I've decided I'm just going to point it out. This is cancelled. Sorry. I am not writing anything more in this vein. My blog has a little bit of what was intended, though.
Take Fallout. Extrapolate, instead, from modern day, rather than the 1950's. Extrapolate using 'hard' sci-fi as opposed to 'soft' sci-fi (Hard explains the science and is somewhat more realistic, soft says 'because science.'). Take an engineer from this world of hydrogen bombs, apocalypse, superbacteria and quantum entanglement, throw him in a hazard suit and then chuck the package into Equestria. That's about the plot of this. I'll run through the episodes with him added and my own adjustments to the personalities of the main cast (not all that much, but stuff like Lesson Zero and the book episode just seem to break suspension of disbelief for me). I had an urge to write something using this post-apocalyptic world I created, and this was the only good story site I knew, so I threw in some ponies. Or rather, threw it into a vat of ponies. I'm new to stories here, but I think I have the tags down. Tell me if I've made some mistake.
DISCONTINUED on account of my soul going on strike because of this. I'll write down some of Green's adventures in his homeworld on another site, and I'll post the link on my blog later.