What impact will Windows 7 have on compatibility test matrices?

In an InfoWorld article titled Microsoft confirms IE8 kill switch in Windows 7, Gregg Keizer reports that Microsoft will allow features and applications to be switched off, most likely through a control panel called “Windows Features”. One application that can be switched off is Internet Explorer 8. The engineering details on this change can be found on the Engineering Windows 7 blog.

Given this ability to switch off individual applications, what effect will it have on testing products that may depend on the switched off application? If an installer or other application expects a web browser to be available for certain functionality, e.g. help info, what will happen when IE8 is switched off? Some applications depend on browser "objects" to be available for custom views. According to Microsoft, this should not be a problem:

"It is worth describing the details of “remove” since this too is a place where there are engineering and customer decisions to be made. We’ve already seen one decision which is to make sure we keep the features staged for future use so that a DVD is not required. A second decision is that we also continue to support the APIs available for features where these APIs are necessary to the functionality of Windows or where there are APIs that are used by developers that can be viewed as independent of the component. As many of you know these are often referred to as “dependencies” and with Windows the dependencies can run both internal to Windows and external for ISVs."

I would expect there to be problems and would want to factor in test cases where critical components are turned off. At the very least, an application under test should gracefully handle conditions where an expected component or API is missing. It remains to be seen as to how this will affect existing applications, and I recommend that some level of compatibility testing be done against legacy products just to be sure Windows 7 has not broken your already shipping products.