According to a reply from an engineer on Microsoft's Developer Network forum, DirectX 11.1 will be available exclusively for flavors of Windows 8 only. There are apparently no plans to release 11.1 for Windows 7 or Vista. "DirectX 11.1 is part of Windows 8, just like DirectX 11 was part of Windows 7. DirectX 11 was made available for Vista .... but at this point there is no plan for DirectX 11.1 to be made available on Windows 7", the post reads.
Update (11/14): A slight change of plans may be in the works as Neowin reports that some DirectX 11.1 features have been quietly included on the "Platform Update for Windows 7 Service Pack 1" that is part of this week's IE10 preview release, but is limited to WDDM 1.1 drivers on Windows 7.
Although this information comes from Microsoft employee David Moth, it's important to note that Microsoft itself has not provided an official statement on the matter. Having "no plan" doesn't necessarily ensure it won't happen either -- but so far, it doesn't sound good for Windows 7 users.
While Microsoft has often neglected older Windows operating systems when it comes to the latest versions of DirectX, omitting 11.1 from Windows 7 may have caught developers off guard. Microsoft launched Windows 7 with full DX11 support, eventually adding even Vista to the list. Considering this latest DirectX version is incremental -- 11.1 as opposed to 12 -- dropping support for both Vista and 7 feels like an maneuver powered by planned obsolescence more so than absolute necessity.
DirectX 11.1 is poised to make a significant number of changes to the graphics API, but most of the improvements appear to be performance enhancing tweaks. RockPaperShotgun does note one unique feature that DX11.1 brings to the table though: native support for stereoscopy (read: 3D glasses support). This means the small community of gamers willing to don 3D glasses may be doing so in the future without relying on proprietary technologies from GPU makers. Of course, those gamers will need Windows 8 and titles which support the new DX-based 3D standard.
Will the absence of DX11.1 for Windows 7 force droves of users to Windows 8? Most likely not. However, for some gamers, it'll be one more item to consider when it comes time to upgrade.