I really have to wonder if the claims that it'd be easy to implement is just an attempt at trolling or a joke. If you take a gander at
http://bay12games.com/dwarves/dev_now.html, you'd see that components necessary to 'empire' mode are taking weeks to implement.
That's not really the point I want to make though, the key issue I see here isn't how long 'empire mode' would actually take to implement, it's that it is already in development. Toady is working on the army arc as we speak.
Be it months or years from now, there'll be a time when every adventurer has a whole back story and history that is 'real' within the world's history. It will also have leaders that actually do something. Once that is done, all that's necessary is a choice to pick a civilization leader as your adventurer, and there you go, you're the ruler of an empire without requiring starting out with one settlement, and without having to earn the title as an adventurer.
Consider also Dwarf Fortress' track record of moddability, and it should then be feasible to get it to generate just about any kind of empire you'd like. It might not generate like you'd want every time, but you could make lots of worlds and pick one that looks good to you.
I do think you'd be kind of cheating yourself by not making the climb as an adventurer or as a settler. Without the journey the payoff is a lot weaker in my opinion. But, options are good, and after you'd already made the slog to the top once or twice you're not missing out so much by skipping to the mode you want to play.
[ March 29, 2008: Message edited by: Stromko ]