You would have to contact Zimbra to ask them what their plans are.
Personally, I don't see them releasing any mobile sync features for the free/OS edition. Nor do I think they should.
If you need to access your calendar/contacts/tasks over-the-air, using the free/OS version, then login to the web interface. Works quite nicely on my ancient Sony-Ericsson w580i which doesn't support ActiveSync or the Zimbra Mobile Java client.