Unless I'm horribly mistaken, the XBox runs a highly modified version of Windows 2000 and has a C++ compiler. Thus DF could reasonably be ported to it, although there are definitely some concerns to be had.
For one I strongly suspect that the OS interface would require some work, even if it's a modified version of Windows. I've never coded for a console before, much less an XBox, but I suspect that things like the standard message pump and process entry points are all handled differently. I think it uses DirectX natively, but I don't know what graphics API DF uses. I suspect it's OpenGL (SDL version anyway), which means more porting work... Input would probably have to be reworked too, but the XBox does support keyboards so the interface actually wouldn't need all that much work.
And from my understanding most if not all consoles don't provide any explicit memory management system since general purpose memory managers are too slow for games and developers end up writing their own anyway. So that's a nontrivial amount of work.
So... yeah, in the end, it's way too much work to be worth it. Maybe some day when the game gets to at least version 1.0 Toady might consider branching it to consoles with open development kits. Which is another issue actually... I doubt the XBox will run games that weren't built and signed by its devkit software, which is surely ludicrously expensive. The alternative is XNA, which to my knowledge is C# only.