Besides, unlike many people think, Microsoft does not oppose open source in general.
Even so, I think both you and I agree that Microsoft will try and sue the person/company who releases an official MSX emulator running an MSX-(compatible)-BIOS.
If it's just an MSX-compatible BIOS Microsoft will definately not sue. Commercially seen this is not interesting since the served market is small anyways, and judically seen they don't have a case at all, they don't (can't) own the patents of the bios-design, so there's nothing to sue about.
Especially not with the precedent set by Compaq, who reverse engineered the IBM PC BIOS and started manufacturing IBM PC-Compatible computers which gave rise to the PC industry as we know it today.
Ofcourse reverse engineering the MSX BIOS cannot be done in the USA, because under the DMCA reverse engineering is strictly illegal. sigh
