DirectX 9.0 4.09.00.0900 (RC4) December 19, 2002
DirectX 10 6.00.6000.16386 Windows Vista exclusive November 30, 2006
DirectX 10.1 6.00.6001.18000 Windows Vista SP1, Windows Server 2008
DirectX 11 6.01.7600.16385 Windows 7, Windows Server 2008 R2 October 22, 2009
DirectX 11.1 6.02.9200.16384 Windows 8, Windows RT, Windows Server 2012 August 1, 2012
DirectX 11.2 Windows 8.1, Windows RT, Windows Server 2012 R2, November 2012
so yeah, it has been getting aggressively more 'frequent' since 2011.
Directx9 lasted 4 yrs
Directx10 lasted 2
Directx10.1 lasted 1
Directx 11 lasted 3yrs (which is what everyone is use to.)
Directx 11.1 lasted for 6mths
Directx 11.2 probably for most 1 yrs
then Directx 12 will come in late 2015. (rumors)
just earlier this year, AMD came out and said there will NEVER be an Dx12
but Microsoft basically came out and said AMD's statement is BS.
http://www.hardwarecanucks.com/news/amd-roy-taylor-directx12/
If you ask me, which you hadn't.
but I will answer anyway. the best time for MS to launch Directx12 will be on the 'NEXT' gen of Consoles. XBOXtwo ?
there are lots of specs about what changes they really need from Directx11, and the answer is 3D.
Most people are calling 3D pointless now, but that's what people said about 3D in movies some 3 years ago.
people have a tendency to blast down new tech disregarding the trend. 3D gaming is COMING, and if you want an early piece, Nvidia 3D vision is a good start.
This is an area AMD need to catch up as well.