Yup, its gonna do a Duke Nukem Forever.
Not quite. Duke Nukem Forever was officially announced back in 1997 and TES5 hasn't been announced at all. A small, but very important difference.
Now supposedly the Moderators here weren't given 'any' insight into the future of TES (just as ignorant as us) but you seem to know something significant.
It's simple logic really.
Morrowind was announced in 2000 but not released until 2002, two years later.
Oblivion was announced in 2004 but not released until 2006, two years later.
Fallout 3 was sort of announced in 2004 too, before Oblivion, but only because it was about Bethesda buying the Fallout rights from Interplay which is a public company. They didn't really talk about Fallout 3 until early 2007 and it was released in late 2008, almost 2 years later.
So with all their blockbuster games, it taken about 1.5-2 years from official announcement to release, and whatever big game they work on now (which probably is TES5) hasn't been officially announced yet. And there's no chance it will take less than a year from an official announcement to release either, none at all.