The real issue with sim graphics is that they are inherently detrimental to the system, no matter what you're running. The reason being thus:
If you look at 3D environments such as FPS games sport, they are small. Less than a square kilometer in a section. Yet that is the detail we are asking for . . .
So we have to make a compromise. Quality for quantity, with quantity being the absolute.
Of course, this could be conquered by online simming being the only option. You could have beautiful landscapes that were extremely detailed that would be downloaded by the sim as you are flying over. They could be graduated down by LODs, but you would always be able to get intense graphical quality when you get down to low levels because of the downloads. Of course, this hinders the breadth of consumerism tremendously. You would lose a large portion of your fanbase just by doing this one thing. I myself would never buy this sim for that reason.
However, an alternate way is possible. Similar to the autogen of the past few years. Any area that is unknown would automatically be filled in by autogen scenery. And not just buildings, but natural land features as well. You would encounter random land features based on local environment. For instance: in the central US you would have waving waves of growing things (grain, corn, etc) when you get low enough to see them, and in places like Siberia you would see snow flurries kicking up when you get close to the ground, as well as drifts in random areas.
The only other option is to have a sim that sits on your HD like a cow and takes up 50+ gigs. Full of total realism and slow framerates because of the massive amount of time it takes for the comp to figure out what is supposed to be there and to render it according to onboard plans.
Either deal with low realism or concede to full online flying. Those are your only real options.