I can't seem but find myself bothered by upcoming solution for difficulty levels in Steam DF. Slider options before you start the game just seem too uneloquent for me. First, it distances itself from actual simulation which is the main point of DF. Second, sieges are not part of the main difficulty aspect of the game at all. Soon after losing the first siege, most of the players learn some survival exploits to overcome them anyway. Difficulty sliders will lose their actual meaning in no time here.
But we all need some measure of control in fortress settings right?
So here is how I would see the solution... and at least in my brain, it seems simple enough to implement.
Let the siege triggers that are tied to traded wealth remain, no need to change that and this is what it seemed like most players wanted anyway.
But let's add another simple mechanics...
Before you embark, the game calculates how many fortresses belonging to your civilization are nearby. If you embark near the other fortresses of your own civilization, the siege triggers will be set as an easy mode. If you embark in far distant lands, far away from your own civilization, game will be hard mode for you.
The logic is simple - the enemies see secluded fortresses as easy gain and probably think twice before attacking a fortress which is surrounded by cluster of other fortresses.
Now before you embark, you make a decision - do you want to trade more embarking freedom for more security and in what proportions?
This adds simple geopolitical aspects to the game that determine the difficulty. And even choosing your civilization will matter more.
What I also find good in this solution, is that the difficulty settings can even dynamically change as fortresses nearby will fall or rise. And it is probably slow enough that it won't cause too unexpected surprises to more anxious players.