so all that said, I can envision a strategy where CI (I lump CD into the CI bucket) can use SDF to deploy (shared db) customizations on change, with some other mechanism to test/deploy code on change. Maybe the CI system could keep track of code/schema relationship similar to what it would do for a non-NS project.... some of this is me thinking out loud here.. 🌤️

That's one of the options we are currently evaluating in the context of CLI and testing framework. If CLI would be able to deploy and run unit & integration tests in a NetSuite account, you could create a workflow like you describe in a CI environment