Update: VMware have release Version 5.5 of vSphere not vSphere 6 in August 2013.
The vSphere 5.5 release will offer new and enhanced functionality to deliver efficiency, agility and resiliency for customer IT environments strengthening the ability to run business critical applications at high service levels,.
• Availability and Performance, Storage, Scalability
vSphere ESXi Hypervisor runs directly in moory and an error in memory can potentially crash the system. An improvment on how to handle this would be a welcome addition.
Improvements in Hot swam. The ability to hotswap between SATA discs is a great feature of vSphere. We believe some improvment is needed on this to allow for SSD devices as these are now more relevant.
vCenter Server Enhancements:
The vSphere Web client has seen improvments in previous versions and we believe VMware will continue to improve on this interface allowing for better features.
vCenter Server Appliance has improvements as well in each version of vSphere. We have always been concerned about the embedded database and would like to see improvements in this area.