This tool gives us a degree of map customization we've never had before. All map features save rivers and HFS are now editable. I love it.
As far as new features, here's a short list:
pits of radius greater than 16
winding chasms
adamantine tubes
roofless pits
It looks like features are currently restricted to one map block. The new "range" feature in dfliquids has some code in it to allow rectangle-shaped masses of water, magma, or obsidian that cover several. I'm not sure if this technique can be used for your more complex pits, but if you could provide a faster way to get pits of natural size or bigger that would be cool.
With a bit of elbow grease we can use the current chasm tool to get the winding chasms of 40d, but do you think there might be some way to designate a chain of map blocks and create narrow connected chasms automatically, or for us to set up an ascii map and use that?
I know we discussed adamantine tubes before and the difficulties of creating features of certain materials, but if there's any way to declare a new local feature, would it be possible to generate adamantine veins, possibly turning hollow at some random level?
Finally, the fact that this isn't a feature yet seems to imply that these features need a roof to be generated, but if that's not the case, being able to toggle roofed/unroofed pits would be a nice addition to the options.
I don't know how many of these are feasible, and I'm sure at least a couple are huge projects, but there's not many other improvements I can think of. You do awesome work!