It would be great getting H2 database support:
The database can run in an embedded way similar as HSQLDB, but the storage format and the database is more efficient, which makes it suitable to permanently run in production systems. For some use cases I do not want to deploy a separate database (simpliness: Docker image without need to deploy another DB, but storing larger analytical data). HSQLDB is pretty inefficient when storing records (the entire log is stored until the database restarts).
H2 database is also supported by Spring Boot and JPA.