Citing Stefan Brüns post on kde-devel ML:

How about using one db per partition? This has several benefits:

• you free up space for 64 bit inodes (currently 32bit inode || 32 bit device)
• UUIDs are large in general (128 bit), adding this to the document id means

considerably larger keys to compare.

• the db becomes movable, i.e. saved on external drives
• as a consequence, the db can also be saved inside a vault

That would eliminate a major flaw: Baloo cannot uniquely identify removable drives and network shares.

The longer I think about it, the more appealing this approach becomes. It' a huge task though...