The next TES game should be set in Hammerfell, then BlackMarsh, Elswyere, Valenwood and Summerset Isle. They wouldn't be able to do some of these places justice if they made them right now. Assuming the next Elderscrolls comes out in 2016, a desert wouldn't be too hard to pull off and we've barley touched Hammerfell in this series.
They've already done Hammerfell - Twice.
yokuda sunk and atmora is too cold to live on, but the mer home-land might still be around and akavir is always an option
The only "mer home-land" that ever actually
existed is Tamriel. The "Aldmeris" place is just elven delusion.