We don't know.
Also, please know that gamesas is tight-lipped about any ongoing projects; they won't tell us about new games until E3, and they don't tell us about new DLCs until they've finalized a release date. We only know about what they plan to release when fans investigate what is added in patches, and carefully watch what copyrights gamesas takes.
What we can certainly say is that as of patch 1.9, there is no evidence that gamesas is working on any more DLCs. Rumors persist that Hammerfell may be the next DLC site, based on gamesas renwing the name "Redguard," but most fans belive that they're simply securing the copyright name, not making a DLC based on it.