I have. (Sort of.) It seems like it'll never get clean enough to release, though. Here's Elena from 3rd Strike on NES
It doesn't exactly focus on the fewest number of sprites, though. It tries to find a balance between sprite tiles and sprites. It's definitely not as good as one can do manually in either area, but for stuff like this it's a benefit just not doing it manually.
The algorithm does guess palettes (even if sprite overlays are needed), but it's worse at that than other things.
tl;dr: Import a frame sequence for a large character, get exported data in an NES ROM. But there's not too much about the algorithm that's NES specific. It could work with palettes of 16 colors and different sprite sizes or whatever with some tweaks. I do have plans to make it focus harder on fewer sprites, but I'll probably never computer science it out enough to try lots of stuff to get the absolute lowest sprite count.
Edit: Here's its process for taking the tiles:
It does one pass to guess palettes (if you don't provide a palette), then eats away the sprites from the corners.
Edit2: It also does "deep deduplication" to further reduce tile count. I don't remember if that's reflected in the tile count above.
The example I give is this image:
All of those are the same tile, just offset or flipped differently. "Deep deduplication" would make all uses of all those tiles into one unique tile.