What is it good for
If you read what adobe has to say about the app you'll discover that it is currently incomplete and that they are asking for feedback. So it is, by Adobe's own words, not as good/usable as they'd like it to be and would like to make it better/ more useable. I can only imagine that anyone working with digital negs, who shoot in quantity and or for those in a small production environment would want to test this software and offer feedback. This is a pretty rare opportunity; one I hope it is not lost on the folks doing work in greyscale and those who shoot or handle a great many images.
Why is Adobe Building it...
Adobe's reasons for producing the app may be so that they can sell an inexpensive, full featured app to a small market. At one time HP sold a greyscale only image editing application. This application also ran against the mainstream, as it was being sold just as the DTP world was moving into colour. The HP application was exceedingly good for the time.
There is also a possibility that the application is a bit of a skunk works. It could be they have a number of benched developers and someone was able to promote the idea to the powers that be.
It might also be that they are using it as a test bed for future image applications. In as much as Adobe has labeled PS as being in version 9 (CS2) some might argue that there has only been about 3 major revisions of the application. This means that there are a good many legacy bits and pieces in the app that only a complete redesign and build could fix. Better to test their ideas on a small scale rather than on one of their flagships -- they dont want to re live the Pagemaker/indesign fiasco.
As mentioned in another thread the link to this application and other goodies by Adobe is
http://labs.adobe.com/