Thinner is in in apple's mind. I doubt it will get any bigger, or smaller, so I doubt that there will be a dedicated graphics card.
Give me better speeds and Santa Rosa and I'm game. Id like dedicated but it would throw it into another price bracket and TBH I doubt it would fit.
Apple could do what they did with the MBP. Those have NVidia 8600's in there. Therefore, they can fit it in the Mac Mini.
Edit: Heat can factor in but they could switch the casing to be all aluminum like the MBP is to conduct the heat out a bit more.