I don't believe that Microsoft will ever get to the point of pushing out BIOS/EUFI updates. Nor do they need to...
As far as I know...
Windows has the ability to warm patch microcode on boot using the mcupdate_GenuineIntel.dll and mcupdate_AuthenticAMD.dll drivers (located at C:\Windows\System32) on boot, for Intel and AMD cpu's respectively. On my system the current versions are:
Attachment 176356
These drivers are simple blocks of microcode and cpu identifying information - contain the latest microcode for the system cpu during boot. Windows loads the microcode from these drivers instead, overwriting the microcode that is included with the firmware, without being committed to flash. This takes place prior to the Windows initialization, so, seemingly there's no partial exposure issues.
The draw back of having the latest microcode in the driver is that, at the time of reboot the latest microcode is lost. While for most people, this is not an issue; however, should one re-install Windows (starting fresh), the microcode maybe vulnerable to Spectre and other exploits, if and when the the BIOS/EUFI has not been updated that includes microcode that not vulnerable. Once the reinstalled Windows updated to the latest patches, it may have the latest microcode in the driver and no longer vulnerable. Provided Intel gets their act together...
This is not a specific process that exists in Windows only, other operating systems, like Linux, MacOS, etc., act pretty much the same way on the x86 system with BIOS/UFI/EUFI firmware. One could make the argument that other operating system have been doing this longer than Windows...
Personally, I don't see the need for updating the BIOS/EUFI with the latest operating systems. If the motherboard manufacturers have the fixed microcode for Intel/AMD CPUs, so will Microsoft and they will push it out with the next update. Relax people...