Currently, you can use dbtype / dbname as a shorthand for the archaic classname / subprotocol / subname style of driver specification, but only for dbtype values that the library already knows about. It would be great if there was a shorthand way to specify the driver classname for drivers that the library doesn't already know about.
And this all needs to be documented better (both in the readme and on clojure-doc.org).
One possibility is to allow classname to be specified and to override the lookup-via-subprotocol, as is done for the legacy style db-spec. Another would be to allow dbtype to specify both subprotocol and driver class name, e.g., "somedb/com.whatever.Driver". The former feels less "magic"