Naive question incoming: Does a good modern camera with a macro lens, shooting from a few inches away, have a higher effective DPI than this scanner? If so, is the only problem trying to get a predictable, smooth grid of pictures from such a camera to stitch together? And if so, couldn't you just stick the camera to... a CNC machine, say? Is that not a thing?
When you get down to it - a scanner is "just" a really specific digital camera with a film holder. The problem is that quality is more about setting up the entire system consistently (film aligned on the scanning camera focal plane correctly, can shift from frame to frame, etc). As with all photographic setups, the chain is only as good as its weakest link.
It is probably possible for any single person to build, through sufficient time and effort, a "better" scanner than any model manufactured - but once you are spending that much time and effort on it you've "lost the plot" of the whole effort.