  Virtual worlds have become global platforms connecting millions of people and
containing various technologies. The development of technology, shift of market
value, and change of user preference shape the features of virtual worlds. In
this paper, we first study the new features of virtual worlds and emergent
requirements of system development through trend analysis. Based on the trend
analysis, we constructed the new design requirement space. We then discuss the
requirement satisfaction of existing virtual world system architectures and
highlight their limitations through a literature survey. The comparison of
existing system architectures sheds some light on future virtual world system
development to match the changing trends of the user market. At the end of this
study, we briefly introduce our ongoing study, a new architecture, called
Virtual Net, and discuss its possibility in requirement satisfaction and new
research challenges.
