Just stumbled on this link to a list of VMware Tools version numbers, which shows that the new ESX version will probably be the 4.1 version:
# VMware version-mapping file.
# This file provides a one-to-one mapping between VMware Tools for
# ESX/ESXi version-number codes, and paths to OSP repositories suitable
# for that Tools version.
8289 ../unsupported/tools/esx/4.1
8288 ../unsupported/tools/esx/4.1
8194 esx/4.0u1
8193 esx/4.0
8192 esx/4.0
7304 esx/3.5u5
7303 esx/3.5u4
7302 esx/3.5u3
I saw the same details in some road map documents at work. Also said that it might hit in June.