Well I have learned in this discussion in the Cooker forum and on IRC that relatively speaking I did not know much about “lightweight” desktops. Lightweight in this context can mean size of the installed system (that’s what I was thinking) or the size of the ISO itself. Then in reading I discover that to some people the important considerations are memory and cpu usage.
So far the desktops mentioned as candidates for a “Basic UI ISO” to give it a name are IceWM, openbox, fluxbox, and Lumina. I suspect any of these would do the job though I tend to think of IceWM in this role as I have long used it as a backup desktop. Some distros like openSUSE and maybe Fedora install it as a backup as well. As I remember it Mandriva did this but my memory about this and Fedora may be incorrect. In reading about the 4 mentioned here I start to think that Lumina might be as good or a better choice than IceWM. But I have not yet used Lumina so I’d need to try it first.
On IRC the consensus seemed to be that this Basic UI ISO should include a web browser. Falkon was the only one mentioned as it is most lightweight browser in OM repos.
The biggest feature of the Basic UI ISO, if we do it, would be not what it contains but what it does not contain.