Last night I discovered that someone else had nearly the same idea at nearly the same time, and has been working on it since then, whereas I have just been thinking about it. It was kind of disappointing to realize that I was no longer the lone mastermind behind the idea.
Luckily, that someone else is a good friend of mine. He has also kept quiet about his idea for the most part, so only he and an artist friend of his know about it. I happened to mention some of the research and thought I had put into my idea, and he immediately recognized that it seemed similar to what he was working on, and showed me what the two of them had put together so far, which was impressively ambitious and had a lot of good ideas that I hadn't thought up on my own. The more of his stuff I read, the eerier it seemed -- so much of their design seemed to have been plucked straight out of my idle musings.
So while it was a bit disappointing, it's also exciting, because a team of talented people actually working on the idea will definitely get farther than I would have gotten by myself. I hope I can actually contribute something useful to their project now, and that eventually the idea will become a reality.
If it does, I'll let you all know.