True client-side Shamir shares. Today's K-of-N approval is server-mediated: the server enforces the policy while the data key stays whole. Splitting the key into per-signatory client-encrypted shares — so the server itself can't reconstruct it — is the next defense-in-depth step, and the one remaining item from the original roadmap.
Audit verification cost is linear in the number of live rows. Archival bounds that set, but a single audit --verify still recomputes the whole live chain; there is no incremental/checkpointed verifier yet.