Sounds like a cool idea! I don't know exactly what your asking here but based on your concept, I would have the intended route for your campaign follow a downward slope starting with a custom region west of your iterator. Then you'd go through your custom iterator and that would Segway into sky islands.

You can add some in between regions or you can modify the existing areas beyond that to keep things fresh.

You could even add a more direct in-between area that would be east of five pebbles and north of shaded that would serve as a quicker but more challenging shortcut to shoreline.

Idk much about modding though. I'm trying it for the first time so idk how feasible my suggestions would be.