It can be. We want to move away from IV-based encryption primitives to tweak-based primitives for each individual file. This is just so more people understand how it works, especially since now XTS is a recommended standard. Right now we use a custom solution, which made sense in 2004 but now that XTS exists we can switch over.
Wait, XTS is a standard recommended for block-level disk encryption. It's not a recommendation for file encryption. The two problems are similar, but not identical; for instance, block encryption has strict requirements on ciphertext size, and requires the capability to modify ciphertexts instead of just re-encrypting. Are you sure XTS is a good idea for file encryption? Wouldn't a simple AEAD mode do the job just as well, and also provide for file integrity?
