According to Bogomil Balkansky, senior director of product marketing at VMware, the naming convention for the future ESX Server (or ESX Servers, as the case may be) has not been set, even if people are referring to this future product as ESX Server 4.0. He says that there will be some product rebranding in 2009.
The current ESX Server hypervisors support up to 64 GB of main memory to be allocated to a single virtual machine on a server, and the VirtualSMP feature of the hypervisor (which allows a VM to span multiple cores or processor sockets) can only span up to four x64 cores right now. Balkansky says that in 2009, the hypervisor will double VirtualSMP capability to eight cores and with quadruple memory to 256 GB maximum per virtual machine. By the way, that is cores, not threads. While the ESX Server can certainly see and use multiple threads in a processor core, if they are there - some Intel chips have virtualized threads created by the chip hardware to boost their efficiency, while Advanced Micro Devices' Opterons do not have simultaneous multithreading (which is silly, really) - these threads are not seen by the hypervisor as a core even if applications riding atop the operating system treat threads as if they were separate cores.
Read the full interview by Timothy Prickett Morgan at Channel & Register