Most of the improvement opportunity is in the offline-first the cache or fast reads already have lots of solutions by using zero I lock my self in thinking in your library's design language and not in terms of what I already know that is raw SQL. If your happy/convenient/recommended path is ZQL then of course people will choose it and only later realize it only works for simpler queries like most ORMs I've been burnt by prisma before and now I don't touch any ORMs and simply use raw sql + sqlc (type safety + auto repo layer from your query.sql)

I would use these DSL if they provide 10x improvement but it seems to me like a downgrade in every way I will need to rely on you to keep this thing running 10 years down the road and hope you are still in business. Whereas raw SQL will probably work as is since past performance is usually indicator of future and sqlite/postgres are 25 years old and if I recall correctly you already had this similar project that is now no longer maintained: https://replicache.dev/ so this by default makes me trust this project less since it will touch critical parts of my app.

Also, imo the custom sync engine path is usually better because most of this turns into logical replication unless you are syncing simple notes and then teams already know what they need and a last-write-wins + row_id,table => changes_log tables isn't that hard the issue is usually that the client and server will need to duplicate functionality and I will be a lot more comfortable duplicating those using raw sql queries since you write those ones and use on both sides. Any half-sync or other optimizations usually just end up causing a lot of headaches in a relational db with foreign keys on.

So, I would use something like this only if it is a sidecar process like litestream seamlessly doing it's thing vs becoming a main concern in my app core. But that again is the issue logical replication vs physical replication and how can a sidecar know the intent.