This API allows modders to save chunks in a world, importing them into another one at requested locations.

Already planned and/or implemented features:

Allow mods to save chunks, include in jar, then place it at specified coordinates in each new world (done)
Allow mods to request a semi-random location for their chunk, for example: Within a 5 chunk radius of spawn, place one of this chunk
Make chunks optionally blend with surrounding landscape including but not limited to biome adjustment, height adjustment, block changes and much more.
Implement a structure saving system (ignore the chunk itself, find special features like buildings and/or chests, spawn it in another chunk)

In game commands:

/chunksave <filename>
or
/cs <filename>

The chunk will be stored as an NBT file in the saved chunks directory, location in your instance root (same folder as the config folder, etc)
As a modder, call the API method, giving it an input stream from the file in your project (assets is a good spot for them) as well as the chunk coords you want the chunk to be placed at. The same file can be used multiple times, though needs a new inputstream for each API call. In the future there will be a way for non-modders to import chunks. In all probability this will involve using filenames to request positions, as well as a folder to place them in.

Static Chunk Manager