I have an implementation of this in Datsync (here), and I'd really rather have it just be a function in datascript.core if you're amenable. More or less, it creates a new database from the old datoms and the updated schema.

There's a question about what the should be sent to listeners when this happens. It could perhaps be a more or less empty transaction report with keys :schema-changes, :new-schema and :old-schema, perhaps.

Happy to clean this up and PR if you like.