It's not the total color count that's the issue. It is the localized color count. That being the NES cannot display overlapping tiles, and no tile can be over 3 visible colors per tile. Furthermore, each tile, including the palette applied, has an area of 8x8 at its minimum. The way they would bridge the gaps is by using sprites, but this art would be employing a severe amount of them, to the point of unbelievability. Not to mention the whole scanline issue.
I guess obvious unbelievability in the graphic limits isn't something new to this project, but damn is it jarring to see. It's really something noticeable, even by those who aren't aware of all the technical limits.