This special interest group (SIG) exists in order to discuss the emerging field of computing in the context of ultra large-scale systems and how such systems relate to or can be built with Python.
The term "Ultra Large-Scale Systems" comes out of the research that was done in 2005-2006 by the Carnegie Mellon Software Engineering Institute's ULS Systems team. It entails the "creation" of systems of the next 10-20 years (and possibly beyond), systems that will be too large for current design, development, management, and interaction practices. These systems will come into being through amalgamated services united to provide solutions for a particular (potentially very large) problem space.
The official report is rather long but is available for free. Shorter summaries are also available. There is one that gives a fairly concise summary, especially on slide 22 and 23. Although that particular presentation's content is focused on defense applications, these problems are of deep interest/concern to industries such as the medical field and other organizations that will have extensive and diverse infrastructure and services operating in diverse and potentially hostile environments.
Another presentation outlines the research that needs to be actively pursued in order to make ULS systems a reality (see pages 69, 38, 37 -- note that the dotted 6.x.y number refer to sections in the official ULS report.