here's an interesting little experiment i did.
now, it's unlikely that this will ever be implemented into dimensionshift, but i REALLY wanted to see how this flows,
so here's a "functional" 4-screen mirroring.
this loads 2 screens of garbage now because the loading code is written vertical mirroring, but even so, you can observe from this that the game does indeed scroll in 4 directions at once, with zero scroll artifacting, and does indeed
utilize all 4 nametables.
for the more technically inclined, the way INL cartridges do this, is by hijacking the 4th CHR RAM bank for the tableloads, which means that tile animations are permanently locked to a maximum of 3 frames instead of 4.
that said, a "perfect" 4 screen scrolling can definitely be achieved using nesmaker and current mapper 30 hardware.
https://youtu.be/jdKRJHXhJpw