There is a wall. We will hit it. Where the graphics cost more to make than the game can sell for.
Of course theres gonna be a wall. They hit some type of wall with core process development and what did they do? They went to multicore parrallel processing. Granted, now software have to be code in a certain way to take advantage of it, but thats the way its heading now to improve CPU processing performance.
The same will happen with "graphics" that you're so worried about. When or IF they ever hit that "wall", it'll drive the need to develop better "tools" and cost efficent methods to create better graphics. Its probably already happening. Don't worry my friend, when theres a will, theres a way.