I don't support the ability to create Mushroom caves, but I do think that resources like copper, gold, gems, mithril, marble, and mushrooms (borrowed from Orbi modmod, where they are a resource instead of an improvement) should be placed in peaks and that you should be able to build mines and quarries in peaks.
Currently, there are SDK blocks that prevent you from building anything on peaks. (Well, if you change the peaks' <bWater> tag from 1 to 0 you can build roads, but not improvements.) It is still quite possible to add resources and improvemnts through python.
I was planning to give Stonewardens a new Delve" spell, which would take several turns to cast but would have a good chance to find valuable mineral resources on the peak and connect it with the proper improvement. Obviously, I'd also be giving Stonewardens the ability to move through impassible terrain. I was thinking I;d do this through a promotion that RoK units can get, and Dwarves can get at lower levels than most.
Now I'm leaning towards instead trying to edit the SDK to make improvements buildable there and to make it possible to build improvements there. I'm thinking that both Dwarven Workers and Miners (the executives of the Prospectors Guild which I'm borrowing from Orbi modmod, which are also able to build mines at twice the normal worker rate) would be able to move impassible and harness the resources there. I may leave Delve in too, but instead make it just improve normal mines by either finding a resource or improving the base yields (temporarily?)
