Abstract: The historical development of hypermedia systems can be characterized as a series of successive abstractions of functionality away from the "core" hypermedia server, often resulting in a new open layer in the hypermedia environment architecture. Recently, this trend of abstraction has been applied to the hypermedia server itself, replacing the notion of a single, closed hypermedia server with an open layer of structure servers. This newest development brings with it a new set of challenges and research issues for open hypermedia researchers. In this paper, we discuss these issues, review some of our collective applicable experience with contemporary open hypermedia systems and other work, and point out some of the more pressing and intriguing open questions that we feel are facing open hypermedia researchers today. We also examine the "split" in the current hypermedia research community between "system" and "domain" researchers and the still-present need for interoperability among systems, and discuss why any attempt to address the issues we discuss in this paper must account for these observations.