I wrote one on taverns, which slightly touched on this topic, but I've mostly written this in response to the suggestions of other people, or in non-Suggestions Forum threads.
Besides, I don't consider my threads "megathreads", although Improved Farming does come close. Megathreads are threads which pull in a list of every idea on a given topic all at once. They're more lists of everything that has been discussed (preferably with links back to those discussions) than a single narrative idea of where any one person wants the game to go. Just being a large thread doesn't make a megathread. (Think of it like the difference between a book in a library and the card catalog with descriptions of the topics of every book.)
Also, I actually have a bit of a list of things I want to write still. I'd like to write a more abstract thread on the nature of player work versus dwarven work, and one on the signal-to-noise ratio of dwarf fortress's information. Mostly, though, I'm gearing up to rewrite Class Warfare.
I consider the mining improvements, Improved Farming, and Class Warfare to be a sort of trio of the basic structure of fortresses, which make all resource gathering and expenditure more deep and entertaining. Mining covers inorganic resources (stone, ore, gems), farming covers organic resources (including wild resources like naturally growing trees and mushrooms), and class warfare redesigns the way that dwarves interact with the player and their fortress, making labor a more tricky subject.
It's not exactly "every aspect", (I could probably write much more about Adventurer Mode,) but it does make up a pretty massive chunk of Fortress Mode.
There's no point in saying much otherwise: I enjoy thinking about and discussing DF in a grand abstract fashion for its own sake. I'm obviously capable of devoting pretty serious time to the topic, and enjoying it. Who knows? Maybe I'll even change Toady's mind on something, or come up with something he didn't know about. But really, I just enjoy thinking about these things, and occasionally writing long posts up about them.