Doesn't have to be native, only fast enough to power gaming, office and extensive image collections. Only one of those requires lots of computing horse and that mainly on the GPU (though there are some offenders like PUBG or Minecraft, the later also slurping up a significant chunk of memory bandwidth)

I wouldn't even bother mentioning X86(64) in the context of RISC-V. When RISC-V becomes financially viable for manufacturers they'll switch. Cost alone is enough to justify the change. Most of the innovation happening these days is in the mobile sector with mobile devices replacing more and more of the average consumer's computing needs. This alone has made for some pretty nimble software already. Every device sold with one of those ARM-based processors has an Arm holding "tax." ALL vendors are happy to not pay that tax and will be even happier to have nothing to do with ARM Holdings at all (I've heard they're shit to work with). Arm and RISC-V are both RISC architecture; not hard for software to switch. What happens in the mobile sector will trickle down to the rest of the tech industry. Microsoft has even embraced RISC with Windows on snapdragon devices. I doubt the consumer will even notice a difference.

I think you are confusing EFI firmware with CPU microcode, the EFI does often contain microcode ROMs to upload to the CPU at boot but the microcode itself is proprietary and signed and reverse engineering is quite a challenge - In fact there was a submission of a presentation here not long ago showing the painstaking progress of a small group of individuals attempting to reverse engineer some intel microcode.

I assure you there is no working libre microcode for intel CPUs and it seems far more likely people will successfully focus their efforts on open source hardware before being able to successfully replace substantial microcode of complex closed source hardware.

In "libre" EFI mods they tend to disable ME as well, maybe you were confusing that with microcode?