I think it would be interesting to have a way to recursively import a local directory without actually moving files around. And to be able to checksum these files as well (without moving them into the annex).
This would work somewhat similar to looping over a directory and adding file:// remotes for each file.
A use case is importing optical media (read-only), whilst keeping that media as a remote, and being able to calculate checksums directly without moving any files around.
For single files, it would also be interesting if addurl had a "--localchecksum" option that would only work for file:// urls, and make it checksum files directly from their source location?)