No new contender is on the horizon. New releases of NetWare and NT will go head to head for the foreseeable future. Unix is the NOS of choice for enterprise applications. It has managed large amounts of addressable memory, clustering and multiple processors for years. Likewise, the most powerful transaction-processing servers in benchmark tests invariably are Unix boxes.
Administrative costs are steep, however.
Unix definitely will not disappear, but its market share will shrink in the midrange market. The Unix world's conflicting factions and management issues certainly leave the door wide open to a newcomer such as 64-bit Windows running on the Merced chip. But that platform will not arrive until next year and will need time to settle down after release. NT 5.0, scheduled for release next year, will do what it does better with additional midrange features. Active Directory Service, for example, will make NT 5.0 much easier to administer on large networks.