I think the first trailer of Horizon (Zero Dawn) 2 will give us a good point of reference.
Big budget, competent studio, competent engine and it should be one of the first major exclusives developed for a single next gen platform.
I don't think any current gen open world game will top RDR2, and TLoU2 will probably end up being the best looking current gen game when all is said and done.
But I don't know how big of a jump we should expect visually come next gen. I don't think image quality improvements will be very noticeable(coming from X and Pro) and I also dont't expect 60FPS to become a new standard in all kinds of games, especially not big budget single player titles. But I think physics, motion in the world, reactiveness/interactivity, volumetric effects and many other things will be used a lot more and at higher quality. Draw distances will expand, facial rendering will improve. And especially animation quality will see significant improvements.
However, a lot of these things currently aren't exactly bottlenecked by hardware power as much as they are bottlenecked by budget and specifically development time and man power. So I think that the visual disparity between big budget titles and smaller titles will grow larger. Especially in areas like animation and the overall quality of details.
It will be very tough for developers to bring these new consoles to their limits, because you actually have to create all the stuff you want them to render and that is A LOT of work. But on the other hand, this could mean that more devs rather decide to go with 60FPS instead of spending a lot more time and budget on maxing out the rendering budget at 30FPS.