One such thing I did get a fair way into was something like Nanite - I called it compressive meshing. It is the typical case of misguided engineering hubris at work.
The initial work looked promising but the further into the problem I get the more complicated the entire thing become. Having to construct the entire asset generation pipeline was just way beyond what I could manage in the time frame that would look anything decent and not blow out the memory required.
I did manage to get something that vague resembled large scale meshes being rendered in a staggered level of detail but it ran SLOW and looked like rubbish unless you hammered the GPU to get sub-pixel accuracy. It was a fun experiment but it was far too much for the hardware and too big of a task to take on as a single programmer.
When Epic showed off Nantine... wow they did what I never could in a fashion way beyond even my best vision! It is one of those technologies that when it came along really was a true solution rather than just hype. Yes there are limits as with anything on that scale but it is one of the technical jewels of the modern graphics world. I have said that if Epic was public traded company I would considered putting in a sizable amount of money just based on Nanite tech alone.