There are already a sparsebundle implementation for Linux, but that’s read-only and only supports FUSE. This implementation is read / write, AND supports NBD (network block device) so the sparsebundle actually appears as a block device on the system, without you needing to loop mount the file in FUSE.
There are some useful things that you can do with a sparsebundle, even on Linux. For example you can rsync an entire a file-system (say, XFS), without losing any metadata. Or you can abuse Google Drive by fuse mounting it and creating a full system on you Google Drive. (rootfs on Google Drive, anyone?)
Get it here.