To call it a preview would seem to be inappropriate, as Apple used the 19th annual Technology & Persons with Disabilities Conference in Los Angeles to let the Macintosh speak for itself on issues of access by the blind. The move will secure Apple's ability to work with the visually impaired and may well catapult them to the top of the heap for people with blindness.
In this first demonstration of features from the upcoming and not yet announced 10.4, Apple is showing off a technology for which they have been laying the groundwork for a few years now.
Although not mentioned in this article from Business Week, Spoken Interface as Apple is calling their interface access capability, is built into the operating system and uses elements that Apple has been asking software developers to exploit since the beginning of OS X.
When Apple moved from the older OS 9 to OS X, they introduced a number of new technologies for developers. First among these is Cocoa, the "new" development system that is tightly related to Nextstep, it's predecessor from Next. However, a bit less visible are what are called NIBs. NIBs are used in Cocoa programs, but can also be used in the older Carbon software as well. NIBs describe the user interface as it appears on the screen in a standard format, and contain a number of cues that can be used by the operating system to make navigation and the Spoken Interface easier for the operating system to handle. Since these technologies have been around since 2000, Apple is already able to show a reasonable level of integration with third-party applications as well as the basic operating system.
Besides the obvious advantage of a standardized mechanism to interface with the spoken interface, the integration of this technology into the next major version of the operating system also means that the price of computing for the blind on the Macintosh will be substantially lower than that on the Windows platform.
Software such as JAWS for Windows provides these capabilities (and a few additional ones, such as integration with Braille displays) using hooks into Windows and a scripting language that allows the company to work around difficulties in particular software, which they do for popular packages like Internet Explorer and Microsoft Office. If your software isn't supported, you can write your own scripts to make it more usable. However, since there's no standard API for the Windows system to speak, each screen reader provider has to work around operating system and application software separately.
And as for the price, JAWS is $895 to purchase and $120/year to keep it up to date. For those complaining about Apple's tendency to charge $129/year for updates to the MacOS operating system, that's something to think about.