Currently Java driver support primitive datatypes and the Java Date.

But as acknowledged even by Java framework people, Joda DateTime is a better than Java-7 provided DateTime framework.

While Java-8 has accepted this and integrated Joda Datetime style, it will be a while before all the enterprise will move to Java-8.

Meanwhile, if Java-driver provides out of box support to Joda-DateTime, it will be enhance mongodb's support for existing Java coding convention, which is to use Joda-DateTime whenever possible over Java-Date.