In my opinion, firmware should be focused on the task at hand : controlling the printer. It should be simple, fast, precise/accurate, reliable and unburdened by extraneous or superfluous functionality.
Since our printers are controlled by our computers, we can consider the file or gcode size to be unlimited. What is lacking in this industry, at the moment, is a way to represent an assembly of parts along with their materials, textures, etc. For instance, I can have an STL file, but there is no provision in that format for indicating different materials. You could have the STL describe surface texture, but that is likely to be inefficient. What would be cool, though, is a format that allowed the specification of surface patterns and materials and then individual objects which reference those things by index. Then you could include the unique pattern representing each surface and have the processing side apply them when the file was rendered, sliced and converted to gcode.
A slight extension to this allows things like mathematical expressions as textures so that you can obtain natural looking surfaces or at least add noise and randomness to a texture. Kind of like procedural texture functions in graphical programming.
Here is the rub, even if these things existed today, most of our printers are not able to produce objects with the required surface resolution to observe that detail. The closest you will find is a resin printer.
That being said, there is the possibility of taking a two step approach to achieve something better than what is possible with FDM alone. The two steps I am talking about are printing, followed up with milling. Say you combined a milling head with a printing head and do one pass that constructs the rough surface. You could then follow it up with another pass that mills out the required material to produce textures that are impossible with our current technology. It would also allow you to produce perfectly smooth, or as close as you could get, surfaces.
I believe there are some professional printers that have this capability. None that the average hobbiest could afford, to my knowledge.