I'm testing enterprise software that does end to end migration from one OS to another. For example, you are on Windows 7 migrating to Windows 8. The IT administrator could schedule a job that will capture profile settings, boot to WinPE to reimage or perform a scripted install, possibly perform driver injection, reboot to the new OS and deploy any additional software. We are updating WinPE to the most recent version but unfortunately vboot Windows 7 and older OS's aren't working on WinPE 4.0 32 bit in vmware. It works just fine on real machines and in hyper-v, so the issue isn't with our solution. This has always worked in WS with previous versions of WinPE until 4.0.
In WS 8, something interesting is my Windows 8 guest (BIOS) works just fine (template of course set to Windows 7 since Windows 8 isn't a version available in the drop down). If I take the same guest, boot from CD, and reinstall windows 7 (formatting the drive), it'll hang while loading WinPE 4.0 32 bit. There seams to be some type of hardware simulation based on how the guest hard disk is configured that prohibits WinPE 4.0 32bit from running.