We are building tonbo: https://github.com/tonbo-io/tonbo , An embedded KV database allows to use S3 as storage backend, and we are trying to implement SQLite virtual table on it: https://github.com/tonbo-io/sqlite-tonbo a real pay-as-you-go DB.
There are plenty of ways to scale out traditional RDBMS, but serverless offerings make it so easy to scale out.