2080 Ti has a lot more power than the 1080ti, it just spends most of it on ray tracing.
Consider the 2080 Ti has 18.6 transistors the 1080 Ti has 12 billion. The issue nVidia saw is games are less limited by polygon counts and 4k is still not mainstream so they needed something else to keep the treadmill going.
4K is a bit of a catch 22 situation - hardcore gamers don't want 4K as the GPUs don't have enough performance for it. Monitors don't support higher refresh rates as there is no demand from gamers for a 144Hz display. Intel iGPUs have supported it comfortably for the last couple of generations, but Windows is still a POS when dealing with 4K, so businesses aren't going to bother upgrading their trusty Dell 24" 1080p monitors anytime soon.
Not really, no. It's pixel density and refresh rate as always, and that is driven from the display.
> Are there any roadblocks in GPU development we'll hit soon?
We already have. The 2080 is a negligible improvement to the 1080ti platform with regards to compute power.