I'd like something like this. Eventually something that generates a save file externally, like an external map editor that will save maps for Slate. In it you should be able to have height editor, color editor, etc., it could be more useful than an live in-game one, seeing you won't lag up the server, and you could do big maps easier.
Let's say you want to generate a 256x256 map in Blockland with such a script in LSG or Terragen:
LSG: Not bad but too linear, only generates one-of-a-kind-blocks.
Terragen: Jet around for no reason trying to generate a big land.
With this external tool you could set some height limits; the overall map being generated somewhere around Terragen, except that it works separately from Blockland, when the generation is done, it's saved in a .bls file, since it does not need the player to be on a server or anything it will also be faster, which could mean generation of huge maps (1024x1024?) of 8x and 4x cubes, yet, this could mean massive brick count rape.
But it could be nice, more client-friendly than Terragen and/or LSG, and faster.
The only con it would be that it won't generate more land over the existing land, and will save it as a separate .bls file.
I typed that in a manner not even I understand, sorry if the same goes for you, if you don't understand tell me and I'll just do a image of an example of how the GUI would look like.