The best move this sim could make right now is to openGL.
Since it's faster (see note below) and has just as much functionality as DX, I'v even seen HDR in opengl (hacked ofcourse).
unfortunately, anyone who actualy uses vista won't be able to play it if that happens because opengl has had its legs cut off in vista.
So now we are back to square one, DX8 or 9.
Aparently alot of game companies HATE DX10 anyway. since it doesn't offer them anything but more code to wright.
Note: On alot of older systems DX caused something I refer to as a memory blanket, not sure if thats the right way to put it though.
This "blanket" was basicaly the fact that DX acted as a layer between your software (game) and hardware, as far as I know this is still how it works. This layer was what alowed alot of windows based games to interact with your hardware and still be monitored by the OS.
On windows NT systems it alowed games to function properly since NT "didn't like" apps interacting with hardware directly and as far as I know that's why opengl didn't work on NT systems.
OpenGL may seem similar to DX but it infact is not, it doesn't have this extra layer, it alows games to use the functions on the hardware without running a check on them first. Where DX would run almost like a filter, GL runs as a direct link.
This information is about all I can remember from what my uncle explained to me about 5 years ago. He told me this when I asked him why my games ran faster in GL than DX.