Three tweets from William Lam of VMware, with more information about new features (and one limitation) of UEFI, including a useful VMware UEFI article:
Excerpt from article:
For those of you who may not know, UEFI is meant to eventually replace the legacy BIOS firmware. There are many benefits with using UEFI over BIOS, a recent article that does a good job of explaining the differences can be found here. In doing some research and pinging a few of our ESXi experts internally, I found that UEFI PXE boot support is actually possible with ESXi 6.0. Not only is it possible to PXE boot/install ESXi 6.x using UEFI, but the changes in the EFI boot image are also backwards compatible, which means you could potentially PXE boot/install an older release of ESXi.
http://www.virtuallyghetto.com/2015/10/support-for-uefi-pxe-boot-introduced-in-esxi-6-0.html
Firmware Security 