Third option: put it out into the world for others to do something with it.

I've had enough big ideas to know they won't be the last. It's better for me to finish what I've started. But if an idea really is a big one, it's beneficial to me for it to be executed upon regardless of whether I'm the one to implement it or not.

So I'll write a blog entry with the full details, and try to spread it around some, and hope that either someone will take it and run with it, or when someone's later searching, they'll find my thoughts and incorporate them into their own plan.