Ah, makes sense. I thought that the rivers might form first, forcing the mountains to generate around/in between them; but if they’re only looking for a viable space around the mountains then yeah they wouldn’t work in the archipelago.
What I’m envisioning would probably then need to be accomplished by modifying the island generation on the archipelago mod, so that it generates tall pillars with sheer or almost-sheer cliffs. I had thought that using the rivers would act as a shortcut, as I said earlier, “slicing and dicing” the islands up like a pizza. However, if that would only give sheer sides like in your diagram, then yeah it would be pretty ugly/hard to believe; and I don’t imagine that “blending” or “roughening” those cliffs after they’ve been cut would be easy to do.
Oh well, just another idea to add to the list of things I really should mess around with one day, hahaha. Thanks for the insight into river generation though!