I don't know anything about rom hacking but is it really that hard to get this to work?
Pretty hard, but I might be overcomplicating it. There are A LOT of little things to do, at least from a DKC1 perspective.
if I recall correctly, the objects that spawned are hard-coded. Also, vram management could be tricky. Because the screen is larger and sprites must be drawn longer, there is always a chance that things aren't spawned because too much exists.
Also, idk but I think tilemaps are hard-coded to 256px wide, but that might be the easier of the evils.