Thanks, Kenton! Really encouraging to hear you find the idea interesting.

Right now I'm focused on Postgres (biggest market-share for full-stack apps). A sqlite version is definitely possible conceptually.

You're right about the bigger picture, though: Cap'n Web + Typegres (or a "Typesqlite" :) could enable the dream dev stack: a SQL layer in the client that is both sandboxed (via capabilities) and fully-featured (via SQL composability).