Good question ;)
For one of the next versions we will add CalDAV Sync support for todos/tasks also.
But there is a pitfall: Reminderfox supports the industry standard RFC 5545 Internet Calendaring and Scheduling Core Object Specification / 5546 iCalendar Transport-Independent Interoperability Protocol (iTIP).
This is supported widely by remote calendar provider like
fruux.com or ownCloud.org.
You may miss the one or other internet player here.
Günter