Ponies are a great thing to write about. I mean, they aren't the best thing to write about – things that you made yourself are the best things to write about – but yeah; it's kind of futile to argue about this thing. That's why, in this giant mixing bowl of the psyche of the human mind (mine in actual fact), this thing popped up in my head and wouldn't go away.
You've all seen these "Humans on Equestria" and "Ponies on Earth" thing; those are fairly standard and are well-worn paths that have probably became entrenchments by now because of all the shoes eroding the land underneath. I wish I could write about these, but you know, I'm kind of not very good at writing things (proficient, but no expert). Thus, usually I have explored concepts that have not been dealt with.
Having a large group of interests help in that, allowing you to see many different things and hopefully alchemize them into something. That's basically how this "book" thing came from: reading about a constructed world from some guy you never heard of, and then thinking how nice it would be if you put random stuff in it and see it react. Just like a chemical reaction! The difference is that each time you do it it comes out different, of course.
Having bothered you with this rampaging monologue that isn't even part of the story, I shall end this with a link to the first letter of the story. From there on you shall find it easy to find the link to Lyr itself.