I think DwarvesH has a point about using someone else's content in the design of your own game. As a programmer interested in that area, I know too well how hard it can be to build up enough content to actually have something for the code to work with. Even for just the placeholders. If I ever went on to make a DF-like game of my own, I'd take DF's raws as base material without a second thought - because I'd know I wouldn't keep using them in the end, but in the meantime they'd provide me a framework I could build around.
Case in point - the SpringRTS engine. Paraphrasing the famous intro, "What began as a project to transfer the Total Annihilation game onto a new engine, escalated into an opensource RTS engine with a million games." SpringRTS began as a simple RTS engine project, utilizing all content (bar maps) from Total Annihilation directly, even from the same archive formats. Content-wise, it was fully compatible. Time went on, people remade old unit models into new ones, then a whole new model format was introduced, and now the only things connecting SpringRTS to Total Annihilation are the folder structure for content, and some variable names in unit files. Even in games/mods specifically meant to recreate the old TA feel, though bits and pieces of the original textures are also used in those. And probably sounds too.
All I'm saying is that using another game's content to help develop your own isn't a bad thing - while you are, indeed, using another's work, as long as you don't plan to pass this work off as your own, you're good. With this in mind, Godspeed, Dwarvesh! Perhaps you can take your game to places where DF dares not tread. (though with the planned scope of DF, I don't think you'll find those places anytime soon. Well, at least you'll have a conventional interface. Earlier, at any rate.