1996 : Dagerfall
2002 : Morrowind (6 years)
2006 : Oblivion (4 years)
2011 : Skyrim (5 years)
Since Dagerfall, Bethesda has had more or less a 5 years development cycle, can we hope a new Elder Scroll in 2016 ?
(I know I know, it's not very likely, but a cat can dream...)