Just been on playonline.com and read the new news! Very exciting, new expansion planned for release in 2010. The new release "Gates of Voldermore" will be Final Fantasy XI's final addition to the long running successful series. There is not much released as of infomation yet but for a few screen shots of new zones and what appears to be a new end game zone like sky or sea from what I can gather from the hints. We are told in order for this expansion to be accessible it will require having Chains of Promathia and Rise of Zillart completed. Can't wait for more news :)
http://www.playonline.com/ff11us/intro/extension.html?pageID=extension