Phoronix found a slide from the recent UEFI Plugfest where Chipzilla’s Brian Richardson talked about the "last mile" barriers to removing legacy BIOS support from systems.

Apparently, the cunning plan is that by 2020, Chipzilla chips will support UEFI Class 3, which means only UEFI support and no more legacy BIOS or CSM compatibility support mode.

Intel hasn't removed legacy BIOS/CSM support yet due to many customers' software packages still relying upon legacy BIOS.

However killing off legacy BIOS support will mitigate some security risks and will allow for supporting more modern technologies, etc.

By 2020 they are said to be "removing legacy BIOS support from client and data centre platforms". This means that the Intel Tiger Lake or Sapphire Rapids release will indicate the death of the legacy BIOS support.