This was the intention for 1.0 as well, but was omitted.
If useCharacterEncoding(or useCharset, or OPT_SET_CHARSET_NAME) is not specified by the application, utf8mb4 should be used.
Connector does not do any re-coding. But it assumes all string data coming from the application to be encoded in this charset, and return data to application also encoded using this charset.
Application still may specify the charset of its choice to use.